I thought the consensus was that the mining devices just need a little extra software onboard to increment extranonce and recompute the merkle root.
I don't know nuthin about hardware/firmware design, or the miner<->pool communication protocols, but it seems to me that should be pretty easy to accomplish (the device will need to know the full coinbase transaction, a pointer to where the extranonce is in that transaction, and a list of transaction hashes so it can recompute the merkle root).