Banks getting involved with crypto is a blessing and a curse. There would be a lot more money in the space which would theoretically increase value. The problem would be with centralization and banks. Bitcoin and crypto currency were created as a way of decentralizing transaction. Banks getting involved would go directly against that and everything would be driven by corporate greed.
I think banks can get involved with the decentralizing concept still intact. The only thing that may happen is that banking as we know it may change!