FUD over PC gaming dying is almost as old as the hobby. I think it peaked when the PC section in stores like Best Buy shrunk to a tiny display area on a couple of shelves. When it used to be 3 aisle on both sides.
PS2 made console super popular again. Then the 360 and PS3 came out with a serious generational graphics improvement. Meanwhile, Steam was far from being a juggernaut. In fact: Many of us were still spicy about physical media dying because we knew this current, own nothing and like it BS, would be the outcome. Here we are.
The number of brands may shrink, and the cost increase significantly, but retail should not die off. Don't forget, Cyberpower, iBuyPower, and all the other S.I.s that don't use proprietary parts. It should provide enough financial incentive to service the market for builder selectable parts.