I've always wondered why huge exchanges like Coinbase and Bitfinex don't just buy a bank. Just drop a few tens of millions USD and cover the reserve capital requirements, and then losing a banking partner here and there won't hurt so much.
Maybe there are some details I'm glossing over.....
It legally probably involves more than just acquiring a small bank. Coinbase has had interest in obtaining banking licenses for quite some time now, but considering that there is total silence from their side regarding banking licenses it's safe to say that regulators aren't keen to grant them any. Coinbase would be a monster exchange if so. I think that bit scares off regulators.
https://bitcoinist.com/coinbase-aims-obtain-banking-licenses/Coinbase was granted an e-money license by the Bank of Ireland this year, but it's a far cry from an actual banking license;
https://support.coinbase.com/customer/en/portal/articles/2928609-e-money-license