3rd party exchanges aren't totally gone, I think the ability to buy L$ is still there, you just can't sell L$ except through the Lindex.
I hadn't thought of blockchain tech being used to process graphics, which is an interesting idea! It would probably be super resource intensive at this point in time though. I was thinking more of it being used to track in world object ownership, inventory, and origination of assets, maybe a better way to fight against copybotting. Also it would obviously be used for the in world currency which wouldn't be tied down to the platform and be freely exchangeable, in contrast to the current situation with the Linden Dollar.
I am slowly starting to see more "game" stuff popping up on steemit, so who knows, maybe someone will build a virtual world on top of steem! Or maybe someone better than I could approach some of the smaller grids to see if maybe there is a way for them to integrate Steem Dollars into their grid?! THAT would be interesting! Instead of putting out a tip jar for donations to cover tier, you could just write a story on Steemit and be covered for the month! :D I think Opensim and Steem would compliment each other nicely!