When will it end. At this rate people will be wanting to play as Hirogen, Breen, and Iconian. A Tholian Bridge Officer (unless it's always wrapped up in an EV suit) wouldn't exactly be practical would it? Besides, if everyone was running around with a bunch of Tholian Boff's, I can imagine the game lagging somewhat more because of the extra polygon construction the Tholians have. That is mere speculation, but I wouldn't ignore that unfortunate possibility.
As for a Tholian Faction. I'd vote no. Before such is even ever considered they've got to fix the Klingon Faction first, and then build a Romulan one that is on par with both the Federation and Klingon ones. That's a lot of work. The fact they've refused Romulan Lock Box ships and have given us Tholian ones would suggest there are no current plans for a Tholian faction, something that personally, I am glad about.
Before anything else gets added I wish they would add all of the other interior areas to the Tholian bridge...and to the other special ships as well. I love the Tholian bridge on my Recluse...but I wish it had more than a bridge.