I think this is very interesting, actually something new in a rapidly stagnating market. It’s difficult to say where smartphone market will go, currently it seems to be cheap throwaway but that seems to be inherently limited.
Could module development be open like application development? This could develop a self sustaining market, hundreds or thousands of different block module application developers. A “secure” block, making your smartphone into a stealth device, this might have significant appeal in todays hysteria. Medical application blocks, this would have great appeal. Automotive blocks, (un)lock, start, locate, routine diagnostics (oil change). Vanity, people like to customize, a huge opportunity to develop limitless permutations of vanity blocks’ colours, textures and materials.
A large potential list, but a fundamentally different market than existing.