Agreed, becoming more primal is certainly an option. To become a 75-25 wolf-human instead of 50-50, much like the “harambear” form unlocked in Legion, would give worgen a tail. In doing so, it would also tick off the Cenarion Circle - who has banned the pack form from use - and would make the worgen far more bestial to the point of a gnoll, capable of low-common and even more prone to instincts. But this is not what most people would want, who want only the tail with no other side effects of becoming “more wolf”.
Another related possibility could be to go about it from the “Horns of Eche’ro” perspective, where the individual does something for the wild god, and thus earns a heritable trait as a reward. To do this well, this would require a questline, where you do something of considerable effort for Goldrinn or his children, much like a heritage questline or the Night Warrior questline. If it was done in this way, then I would appreciate it, and even do it myself.
I would say “imagined” or more correctly “conceptualized”, not intended. If it was intended, it would have been in all of the concept art, not just two pieces from a single artist, Wei Wang, in 2009. There is more worgen art from Lands of Conflict (noncanon RPG material) in 2004, one with a tail and one without.
If you want to look for “intent”, I would suggest looking to Micky Neilson and James Waugh instead, who have been publishing lead and story developer for worgen since their creation, wrote Curse of the Worgen with DC comics, and helped as lore developers with Wolfheart and Chronicle. Waugh also wrote Lord of his Pack, as well as helping with content and world building and script editing.
https://wow.gamepedia.com/Wei_Wang
https://wow.gamepedia.com/Micky_Neilson
https://wow.gamepedia.com/James_Waugh
http://www.mickyneilson.com/about/
Micky Neilson also responded to me on twitter, directing me to the artist - Samwise Didier - for the Gilnean crest, which I found very neat.
https://twitter.com/RedmaneRaedolf/status/937410922175500290
https://twitter.com/RedmaneRaedolf/status/938152359020154881