Streaming will at best be a supplementary means of playing games. Physical copies and digital downloads will remain the norm.
Streaming basically takes the worst aspects of always-online gaming and applies them to all games. Your ability to play is completely dependent on a constant connection to the service. You internet goes out? Can't play. The service goes down for whatever reason? You can't play. The service ends up being discontinued? Well, I hope you enjoyed your time with it, because you'll have nothing to show for it.
And this is to say nothing about all the questions streaming raises in regards to the prospects for long-term availability of titles. Just like how stuff gets rotated in and out of Netflix, the same can happen with video games. And think of all the video games that have been delisted from digital stores because of varying reasons (often rights issues). If a game is removed from a streaming service, you no longer get to play it. At. All. And again, if the entire platform gets discontinued, that means every game on it just goes *poof*. You better hope they're available elsewhere.
I'm no fan of digital downloads, either, since you still don't own anything (which carries a host of issues by itself), but at least you have a local copy saved.