I'm Trying to understand point #2 - It doesn't appear from your posts here that you have had a problem (I couldn't get your website to pull up "Cisco security error") with water ingestion and subsequent hydrolocking from fording shallow water. It seems to me it's fairly easy to determine this depth if you know the point at which air enters your air filter housing. I know this isn't the actual fording depth, but from a hydrolocking standpoint, it seems it would be. Is there somewhere else that water is being ingested into the cylinders? I do understand that you are looking for an official published depth from the manufacturer that doesn't seem to exist, but have you had hydrolocking damage in addition to the oil issue?
Not the OP, but Toyota refused to warranty his motor as "Hydrolocking due to water crossing" was extreme use. He was able to prove it was not hydrolocked by showing parts of the air intake that were clean from muddy/dirty water, so Toyota replaced the engine (That's the summary from memory when I read the website yesterday).
The whole wading depth thing: It is annoying if there are no official numbers. They give these numbers for Hiluxes and Landcruisers.
But still it is just a depth, and if you drive in fast enough you can still manage to break things or make enough of a wave for it to enter the intake.
I would never be confident to have a lot of water through the grill or even over the hood if it is not fitted with a snorkel.
It is annoying that there are no official numbers for the Taco, but I think that is telling us something about the rig. It's worth mentioning that this figure is not provided for most vehicles sold today in the spec sheet and takes some digging to find, and even then, its often conflicting information. The commercials show these rigs driving through water all the time, but one should never ignore the fine print -- "professional driver, closed course, do not attempt" -- in other words, I don't think they care about wrecking a few $40,000 trucks for some advertisement images that will sell them hundreds of thousands of the same truck, so there is a significant gap between what is advertised versus what the vehicle was designed for. This isn't a Toyota problem -- Jeep, GM, Land Rover, etc. all do this to some degree.
I'm quite sure most folks already know what I'm about to write, but the beauty of these forums is folks who don't can find the information they need, so I'll add a bit more not directed at anyone, but may be helpful for others reading this thread saying "Gee, I wonder what the wading depth of my [whatever] is? Should I be worried about this?".
Wading Depth is based on more than just the intake, and while it's a helpful number it's also very dependent on the driver. I know this isn't a water crossing thread but my observations on doing many water crossings myself and seeing many, many more in various videos is this: Often folks go for the Jeremy Clarkson approach to crossing water -- Speed and Power. It looks good in the slow-motion video, but it can really negatively impact the operation of a vehicle that is primarily designed for on-road use. It is better to carefully manage momentum, create a bow wave, and be more like James May - steady and I daresay, slow-is (but fast enough to maintain the wave).
Water in the intake is the obvious first major problem, usually solved by a snorkel if it's installed and spec'd properly -- though there is a video on reddit.com/r/overlanding of some Russian gents who hydrolocked their Land Cruiser because of a faulty snorkel from the other day.
The next problem is water in differentials and other oil-bearing containers. When they cool suddenly, they create a vacuum that sucks dirty water in through the breathers. Even if it's the most pure mountain stream without a spec of dust in it, the water ingress will cause damage as the oil won't lubricate properly. And I've never found a stream without dirt and grime, so there's always the risk of increased mechanical wear and breakdown due to grit in differentials/transmissions. The solution is to install breather tubes that come up to at least the level of your air intake, and make sure the diffs are fully sealed.
Another critical component is the clutch disk and flywheel area. There's always a hole, usually at the base of the bell housing, and that is an excellent place for muddy, dirty water to enter and foul the clutch plates. It doesn't usually cause an immediate problem but over time this ingress will increase the wear on the components of the clutch. Our JK had this happen, and it caused us a lot of problems. You can seal these holes in most applications, but make sure you can un-seal them too -- the holes exist for a reason (For instance, if you have a leaky rear main seal, that oil has to be able to drain out otherwise it'll foul the clutch plates and you'll be going no where, and if the hole is permanently sealed there's no chance of cleaning it off even to limp home).
Perhaps most impactful is what I mentioned earlier, and that is the electronics. If your car has an intake the size of the Eiffel Tower with diff breathers to match, it won't matter, because the ECU and various other critical electronic components are usually not designed for submersion. Even in the jeep JK, which brags about waterproof electronics in the cab, isn't truly waterproof. The ECU is under the windshield height by a few inches, and is not waterproofed, meaning if water is at the level of your windshield, there's a reasonable chance of damage to the ECU's components. Of course, the windshield is very high, and I would never suggest crossing water that deep in any vehicle. But, sometimes the bow wave floods over the hood, and that can get into the ECU. Other rigs are far worse off -- there are reports of folks with ZR2 Colorados, which are sold as the "ultimate off road truck", becoming undriveable after wading through water over the hubs because the power steering unit is electronic, and water ingress into that unit causes the truck to throw codes and not steer. I'll be interested to see if AEV tackled this problem with the Bison, though I doubt it.
Another consideration is the fan. Some folks opt for a switchable, electric fan so they can manually turn the fans off as needed. Cooling fans are designed to move air; they are not robust enough to move water like a propeller, which means when a cooling fan hits water two things happen: Spray gets EVERYWHERE, including on sensitive electronic components that are above the water line, and the fans themselves (and their drive gear) get bent, broken, or damaged.
Don't forget wheel bearings! If you do a lot of water crossings, these should be maintained often -- pulled, inspected, and re-packed if you can. Some models make this harder as they whole wheel hub assembly is one unit, and cannot be easily disassembled for maintenance -- another example of a compromise on a rig.
Other vehicles will have unique foibles for water crossings too. It's very popular right now to eschew traditional gas caps in favour of just two flaps. That doesn't seem very water tight (though I don't personally know for sure), and I've seen a few gas caps go under especially when exiting the waterway on a steep bank. This causes the rear of the vehicle to dip and the filler cap can go under. Traditional gas caps were vented, too, and so they weren't really waterproof but they could be made more water resistant with creativity, if needed -- the newer ones appear harder to do that with. And then there are other components -- start motors notoriously go bad when submerged, for instance, and they are often low to the ground. How many folks bring a spare starter motor with them in the bush as part of their water crossing preparation?
And the final point on wading depth -- it's not just a matter of depth, it's a matter of distance. What I mean is, wading through a metre of water in a well-built rig may be all well and good when the stream is only 5 meters across. But if you have to go
along the stream to reach your exit and it's more like 30 meters of distance you have to drive at 1 meter depth, that changes the equation dramatically. Like a tent, even "Waterproof" vehicles are really more "Water resistant" -- with enough time and exposure/pressure, water will get into critical bits and pieces.
The above is just what I know about water and vehicles and I'm sure those with more experience can provide more information.
The "Too long, didn't read" version: It doesn't matter what rig you buy. Don't go swimming with your car until you've done some work to waterproof it and really understand the vulnerabilities. Some cars will need more work than others. This is a problem with ALL vehicles, not just Toyotas. Buy a boat instead 
OP, I don't think the above applies to you at all, and I hope this doesn't hijack your thread, but hopefully helps others who are thinking about crossing rivers in their cars.
