In the long term, streamed games (Stadia or similar) are definitely going to become dominant. Steam, et al, can still be storefronts, if they position themselves as such – we still need content curation.

All one needs is a screen with support (e.g. smartTV, chromecast, steam box), internet, and controllers. Classic game systems might be needed for another 5-10 years. Controllers & form factors matter (e.g. Switch, VR), but the "power" of PCs & game systems are no longer differentiators.