As others have mentioned we have zero cap space or expansion protection spots to spare, which means any deal would have to
a) return a highly skilled young expansion-exempt player, either at the NHL level or ready for it within a year, who would fit a key organizational need,
b) involve Callahan going along with Bishop as a cap dump, or
c) involve a top-six forward on a great contract coming our way who would be a cheaper replacement for one of our young RFAs, who would in turn be moved next summer.
Even with an extension for Bishop worked out ahead of time there aren't going to be a lot of teams with the cap space to pay him what he wants and the willingness to either give up their top young player/prospect, take on Callahan's contract, or send us a top-six forward on a great deal. And Bish is worth too much to our Cup chances this season to give him away for any less. So I find such a trade unlikely.