In reply to Otto.

Scroll waaaaay down to the bottom of this thread and you'll see John Blackbourn has marked a patch to implement bcrypt as Future Release:

https://core.trac.wordpress.org/ticket/21022

If you can't wait and are using PHP5.5+, then the Roots team have a plugin:

https://github.com/roots/wp-password-bcrypt

We're using that in production with no (known) issues