Speed is only partially the issue the latency is the killer.
With Steam releasing in home streaming devices I don't see the point. It would, probably, be cheaper in the long term to buy a decent PC, game on Steam and then stream it internally than to subscribe.
In fact I don't get why anyone would want to rent a game. I say rent because you never will actually own it as if the service goes offline then you have no game. If the service is down for maintenance or if your internet connection is down it means you can't play a game that you've 'bought'.
M.