I agree and disagree here.
I agree that you will not only need a bridge plate to get on board, and the elevators are going to break (and thus why there's two of them). If it were me, I would have elevators in as many cars that have upper-level wheelchair access and lower level boarding -- and yes, I've spec'ed it out where I have classic bus-style chair lifts that actually *lifted* people up onto the higher level of the bus.
But I'm going to disagree with you with having to stop multiple times because the design allows for travel between said "core". You'll have a lot of attendants and conductors working the elevator to get folks down and out/in and up, but they can do it. Not only that, I've seen both automated ramps and lifts break. And as I hinted above, just two? A double-overnight trip can have them break, and if they break completely, how are you going to get them down a tight set of steps?
It's partly why I took the time to design the consist for my sequel novel (the in-novel "Cougar/Puma" series of passenger train cars). The end goals were:
- Be able to remember where things were while I was writing (very important).
- Be end-to-end accessible by a wheelchair of at most 30" wide (Amtrak gives an extra inch on ether side).
- Go everywhere, coast to coast (including NYP, NYG, and BOS), but have two levels. (Thus using the Bombardier Multilevel as a base)
I didn't have room for automated ramps at low levels. However, I did make sure it had inside lifts and was able to be boarded at a high-block platform like on the NEC. Level boarding there? Only at two cars on the Cougar line, otherwise you're lifting a trap and going up stairs or the integrated lift (yes, there are integrated lifts on almost all the cars bar the baggage car). Ether way, bridge plates are cheaper.