I think they will, soon or late but they will. The cryptos are now moving a lot of $, and this is a great reason for banks to come in.
Where are $ now? Into exchanges.. Where will they be into the future? Probably into the bank's pockets.
I read that some countries accept tax payment via Bitcoin so it's not a remote possibility, one day we will see a small medium and large banks accepting Bitcoin and another cryptocurrency this will happen three or five years from now I read some Ico are creating a partnership with banks.