sys-fs/udisks:2 support should be forced enabled where it's supported, sys-fs/udisks:0 shouldn't be used in any new packages anymore
both can be installed and executed at the same time, which is why they are slotted, so packages that haven't been ported over to sys-fs/udisks:2 yet, don't have to drop their support
but in no circumstances there should be USE flags "udisks2" or both in dependencies, if it's not a RDEPEND-only like || ( sys-fs/udisks:2 sys-fs/udisks:0 )
we have a Tracker bug 439624 open for sys-fs/udisks:0 removal
USE="udisks" is now a global USE flags for UDisks2 (or UDisks1 if UDisks2 support is missing in the package)
Fixed in tree. Ack from maksbotan.