Most people are going to want to build a phone that does what they want and use it. If it doesn't do what they want they'll want to swap maybe one or two things, not everything. The majority of the design is going to be static - yes, you'll want to be able to take it apart but you aren't going to be doing it at parties.

It reminds me a bit of desktop computers: Tired of your slow CPU? Open it up and swap it out. Need more RAM? Open it up and swap it out. It turns "toss out the computer" into "toss out a few chips."

I got my laptop in 2010. It's still kicking okay, but if I wanted to stop the disk thrashing when I open 20 browser tabs, it'd just be a matter of swapping out the RAM. Same goes for faster boots with a SSD. Same goes for compiling and a CPU. This can be repeated until hardware makers decide they need a new type of socket to improve performance.

Outside of tech enthusiasts and niche markets, I see the benefits as less of the present: "lemme hotswap my camera at a party" and more of the future: "I want 802.11ac, lemme toss the radio instead of tossing the phone." "I cracked my screen, lemme replace that."

A little cheaper and a little more environmentally friendly than the current smartphone situation.