The real problem is the case of those with their eight character slots already filled by character from a single faction. They're denied the pet due to its designed implementation, and there's nothing they can do to change that other than delete a character and roll something else. That's fairly messed up.
Additional character slots need to be added at the time the new companion is pushed live in order to avoid such situations.
There is some indication that more character slots will be here before HK-51. By the sounds of the comments from devs on the topic, it sounds like they're moving right along with it.