Could be useful, but I think too many people hate the idea of recurring charges unless it's an MMO where it's expected. Also, you'd have to differentiate between playing and simply having it installed. If it's installed and you get charged while it's installed, you get screwed if you stop playing it but are like eh, I'll leave it installed just in case I feel like playing it soon (which does happen with me from time to time).
In the end, you end up paying substantially more. Within 10 months, you've already matched what you'd pay for the game to begin with ($10+($5*10)...It could be cheaper for people anal about hdd space and make sure to always stay on top of things; but most people who aren't necessarily even Luddites would get screwed royally (one could argue that it's their responsibility to pay attention).
But, like I said...if they could find an effective way to charge based on when played (phone home when loaded?), it could work.