Everything you need to know about the new AL Priority

[Antilaser]

... I'm wondering how feasible it is to wire up a separate JTK/mute button, if it can be done just by tapping the appropriate pins on the RJ45 or whatever it is, or does that information have to be transmitted serially?...

Actually there already exists a variant of AL Control Set that is external buttons Ready. As many European installers prefer such an option for more discrete installs.
External buttons can do JTK just as the original buttons can.