That was the original notion. Although radio probably could've gone into a separate module if they wanted it to, given the radio's frequently a discrete component anyways.

The big change that happened with the "reset" was that the display, primary battery, and AP (SoC) all became part of the frame. The original notion was that all the parts of the phone were modules, all connecting to the AP (which is also a module) via the frame's UniPro network-- the frame itself has little intelligence. (The way this works is actually pretty neat; I hope some of the network stack sees the light of day in some form or another.)

What does AP stand for?

AP or APU stands for Application Processor [Unit] which is more or less synonymous with SoC. The semantics of it are pretty boring, and the term seems a little strange considering modern cell phones are fairly identical to modern computers besides the fact that a few more functions are packages in a single IC.

even if there wasn't a plan to do that, that's how the idea was received. Compare the reactions from HN when it was made clear that you could not upgrade CPU/GPU/RAM/battery/screen individually

https://news.ycombinator.com/item?id=11740451