The base Trail Kitchen is about 18" wide. If you don't have the subwoofer taking up space in the back I would think two could just fit although I haven't tried it.
I'm wondering what you would do with two... two fridges or something else? In a few days I'll actually have two Trail Kitchens here because MORryde is sending me a production unit (my current one is preproduction) so I could possibly give it a try if there's a good enough reason to make me want to remove my subwoofer for the test .
I actually like that idea - my thought is fridge for food on one kitchen, cooler for drinks (or luggage) on the other and more counter/storage space. Obviously you couldn't mount the optional fold out table and clip on table, but you could have sink, stove and food prep facing the rear of the vehicle and a place to put dishes behind the sink on the clip on table. It'd be a good replacement for the drawer systems a lot of people build while also allowing whatever you put on top to slide out for easier access.
My plan with the kitchen is different, I'm going to mostly use a cooler on it as I don't do long trips without my camper (and wife and kids), and on trips with the camper it'd be used for cooking and cleaning outdoors as I only cook in the camper if the weather is really bad. I plan to store water and fuel on the outside of the tailgate door, so would just run a hose from the water there to the sink, at least that's the initial plan. I also have a generator that would replace the cooler on trips where I don't have hookups for the camper and need some power (ie when it's super hot). The camper has a dual mode fridge so no need for one in the Jeep, at least not until we do some longer trips without the camper.