I submit that if that is the case, that those buyers do understand the definition of "Turnkey". Turnkey simply refers to the unit being a complete, ready-to-drive rig rather than the owner buying a pickup, then sourcing suspension, bumpers, winches, etc. from other manufacturers and having those installed, then sourcing a camper from another manufacturer and having that installed, etc. Turnkey means it is already compiled into a ready to use rig.
This is similar to the auto manufacturers offering a turnkey "offroad" or "overlanding" pickup that comes with winches, bumpers, skid plates, high quality suspension, better wheels, larger tires, etc. Turnkey simply means that a laundry list of desirable add-ons come from the factory already installed (and are included in the warranty).
It saves the buyer time of coordinating all those separate installs and likely expense because you are not disgarding items to replace with another brand or spec item.
Once purchased, it's just like any other camping rig (owner-built or manufacturer built) in that it will need maintenance and repairs over it's lifetime.
I 100% agree regarding there being widely-varying degrees of build quality and maintainability across the industry. If the Megatron is anything like Supertramp's Flagship LT model, it will be well thought out, robust and easy to maintain and repair. But we won't know until they unveil the interior and the details of the buildout.
Supertramp just released around their 70th Flagship LT camper and they are constantly refining the design and coming up with new ideas. They are also great about ingesting input from owners, and potential owners, and incorporating updates immediately (rather than waiting for model year changes like assembly-line camper manufacturers). And, they constantly add to the list of available options. I expect the Megatron will receive the same treatment.