I did consider this possibility but I think I preferred the elegance of plain NS, and still highly doubt that Apple will release or has any classes named NSRailsModel :) But I do absolutely agree, it's better to be on the cautious side. It's very likely that NSRailsModel will change in the future.
See the ticket posted somewhere in this thread for more details, I'd prefer to keep the discussion there.
I used the word "inspect" carefully. Apple is probably looking for calls to private APIs by looking at the addresses of functions called in your binary with the addresses of private APIs.
They are probably looking for method swizzling of Cocoa APIs by looking at the address passed into method_exchangeImplementations, class_replaceMethod, etc.
Looking at the symbols within a binary is probably more effort than it is worth and probably isn't going to be very effective.
edit: filed an issue here: https://github.com/dingbat/nsrails/issues/4
Edit: maybe you thought NSRails is an attempt to port Rails to iOS? Please see the readme - that's not the purpose of the framework. NSRails just allows iOS to talk to Rails simply and effectively.