There have already been four different proposals made to fix this (BIP 100, 101, 102, 103) and the miners shot them down. Remember that the miners profit from

There have already been four different proposals made to fix this (BIP 100, 101, 102, 103) and the miners shot them down. Remember that the miners profit from increased competition and tx fees on small block sizes, and they control the block size. It's more probable that banks will use some other system than ACH before bitcoin block size is ever increased.