I think it sounds great (and a bit of sci-fi), but I don’t see corporations like Apple and Samsung allowing this to happen at all.
Not sure about patents but i guess if you don’t use any patents form them it should not be a problem.
The bigger problem is finding companys which work with that, since they probably don’t make that much money anymore if you can just replace some parts of the phone.
Is interesting, but it does not consider one important fact: people love to change their gadgets.
The idea is great! I hope it will come to reality.