GBT was supposed to enable it, but it was supplanted by stratum before it could get adoption. I'm not sure of how to break out of the status quo.
I wonder if a p2p system for mining could be implemented.
P2pool pools hashing but each node still requires bitcoind. It pools hashing but not mining.
I think a system based on fraud proofs might work. All nodes would be mining the same block, but it would be created in a p2p way.