Equating 20% time to murder seems like a bit of an overreaction. Do you do that often?
Anyway, you're asking a room full of developers what they would want and they're telling you. 20% time is a solution that works. Toiling away on the same problem day after day sucks and it gets boring. 20% time breaks up the drudgery.
I suspect that you don't want to solve the developer's problems though, just your own.