Versispellis wrote: »No one can say whether there will be others, until something is datamined or announced. It'd be cool, though.
Gems are the only way to acquire it, unfortunately.
Unclear whether it will return. Some gem exclusives do (pocket watcher pet, for example), but others don't (the long requested gloam wolf as yet.)
Whether you pursue the penumbra wolf is up to you. I have it. It's lovely. Special mount animation and unique VFX and AFX on the howl. A golden dust trails it for a while after the howl, too. It's on par with a radiant apex.