If you believe that it will be smooth and fluid, I have a bridge to sell you.
There's this pesky little thing known as the speed of light.
I mean, even if they were to do the absurd thing of "render X possible futures, send you all of them, have client pick the "best" one", that only reduces general latency, not worse-case latency - and you cannot keep increasing X as bandwidth is not infinite (and their server power is not infinite either). Worst-case latency being (RTT + render time), which is going to be at least RTT. And worse-case latency is what you tend to notice, at least at these timescales.
Will it potentially be useful for those who live close to a datacenter? Sure. (I question the economics of it from a consumer perspective. But that is another matter.) But is it a general technique? No. For example: I have a ping to Google of ~200ms at home. As such, worse-case latency is >=200ms. (Well, again, depends on where the data centers are. But I'm assuming that Google has pretty good datacenters. And almost all of that latency is coming from the "last mile" in my case, which could change.) Are you going to notice 1/5 of a second delay in a FPS? Probably enough to not consider it smooth and fluid anymore. Related: I at one point got annoyed at a projector over Super Hexagon - kept overcompensating - and measured the delay against my laptop's display and found a delay of ~5 frames over and above my laptop. Admittedly, SH is a twitch-based game - but when you're turning / etc in a FPS you want much the same same frame precision. An extra 200ms isn't exactly going to be unnoticeable.
I think there is a business case, even for FPS. FPS are typically played online, so you are already dealing with lag. And a worst case of lag is already going to get you killed, whether the game is streamed or not.
Besides the light is not so slow. I ping Google in ~12ms (from Osaka). Even for a FPS that's good enough for most people, especially if the alternative is forking a non trivial amount of money. I mean most people play FPS with gamepads, so it's not like the threshold in terms of quality is particularly high to begin with.
How many gamers within reach of a datacenter in Seoul? in Paris? in Berlin? in San Francisco? in New-York City? Sure it won't work for you, but that certainly doesn't mean there is no business case.
ping 200ms to google is horrible and more like a dial up modem, with a good connection a <20ms ping is reasonable and if you take into account that 30fps equals about 33ms per frame, game streaming is entirely possible and has been proven to work. Just the economics are questionable at this point.
Is it a smooth fluid experience, or prone to lag?