I used to be all about wanting WoTLK Gold TBC brought back, and hardly cared if classic was brought back - I grew VERY anti-social and introverted over the years of playing WoW since WOTLK’s end, and with that came my preferences of LOW-POP realms and NOT being in guilds other than with what family or VERY GOOD friends I would consider being in a guild together with.

I watch Smooth Mcgroove, both his Youtube videos and twitch streams. He’s one of my favorite people and someone I look up to, because he’s always so relaxed and chill - even when he will start ranting about something, he DOES NOT get angry or rage, or insult anybody, but he gets the point across and is always honest.
When I realize he would NOT ONLY be playing WoW Classic, but ALSO form up a guild and it was open for anyone to join, and he had NO DESIRES to play the game in the manner of “serious, racing to level cap, racing to down raid bosses, progression etc.”, I decided I would roll on the server and faction he was on, and see about getting a guild invite.

The experience, with everything (the faction/side, the server, the guild and overall just anybody I’ve run across in classic so far), has been like a dream come true - an actual godsend. I had become so accustomed to horrible players, fueled by all the emphasis on end-game content and instant gratification (post-WOTLK), that I truly thought hope died for ANY WoW community a long time ago. No, almost everybody who has joined Smooth’s guild, and the servers community, have been so nice and excellent to do things in the game with, and being in a guild where there’s over 900 members, if I ever did so desire to try and do any raiding, I now know I would never care for TBC to come along, to even remotely try and do anything either solo, or along with a few family or friends, like I had originally wished for ever since WOTLK launched.

So, back to my original answer, TBC would never be necessary for what I wish to do in WoW, and I feel that it would take away ANYONE I’d have to do anything with in classic, along with those that would swarm and eat up WOTLK in a heartbeat.
I would not want to say “NO” or deprive those that genuinely yearn for Outland and Northrend’s return, but I’ll admit straight away - I HATED Outland buy WOW WoTLK Classic Gold, and Northrend got boring within a month of playing.