Actually, I don't think it's a good idea. It would be good for people who already mess around with crypto, but it would drive away most other gamers because it would be confusing to them.
But the biggest reason it would never happen is beacuse of Valve's user control and safety. If you observe throughly, everything steam offers is under a very restrict enviroment. From the ingame shift+tab browser to the opened chat links leading to your regular browser instead, they try very hard to keep steam very clean and to not get associated with external influences.
They already have early access as a way to fund new games and devs can always ask users to register on steemit and support them here, though.