To repeat the response I had there: why not just use a scriptPubKey? Since a coinbase doesn’t have input signatures that commit to outputs, there’d be no extra hashing either.
Also note that Stratum v2 spec suggests that ASICs roll the BIP320 version bits, and only pool software updates the coinbase extraNonce.
That’s enough for devices up to 280 TH/s. Beyond that devices could roll their timestamp a bit (though some people believe that should be discouraged) or handle multiple jobs in parallel. Both approaches avoid the need for an ASIC to deal with the block merkle tree.