I think if it becomes a mainstream system it will take its place in the market the same way that PC parts have taken their place. The phone in my opinion is a great platform for modulation. I mean look at the people who love taking pictures with their phone, imagine being able to switch out your camera instead of getting a brand new phone like you mentioned. Imagine modifying a work phone for a focus on battery. I'm not too learned on scope of the project, but screen is crack? Just replace the screen by switching it out. You have the more internal upgrades for graphics, or processing. Like I said though I'm not saying that it will be a hit, but I would love to see a market for different modifications for the smartphone.
I didn't think about modular screens, but that's a very interesting idea to me. I could see a system where I would have the core chip or a module that I could insert into other devices. Let's say I'm at work for example. When I go into a meeting, instead of plugging in a computer I could slide out a presentation module and cast my presentation to the screen. Then using my phone I could view the next slide and control the presentation. From a sci-fi point of view I really like this idea. I could imagine a world where everyone has their "core device" and they interact with the world by attaching their physical modules to different terminals. If a group of friends and I went to a bar, for example, we could plug into a table to hold it while we go dance or get drinks and the servers would know who we are and what we have on our tabs. Of course, someone would be murdered, their core device would wind up in an inexplicable location, and a sibling they haven't seen in years would follow the strings to learn the deep dark secrets hidden in the corners of a core driven world. It could be interesting.
You've got the idea, definitely haha. The project could fail, but imagine a module like you mentioned made my Samsung that allows you to seamless share your screen with any other Samsung product, and also share their screens. You don't need your whole phone to be Samsung just that module. The future of it seems cool.