People don't want Brettons back, they want mounted knights and the knight lances back. Not the Lady, not the Men at Arms and the rest of the army, no one ever used. They didn't fit the aesthetic of WHFB and they definitely don't fit the aesthetic of AoS. Also medival, chivalrous knights can't be copyrighted and that's what was their undoing.
They are the Flesh-eater Courts now or if GW ever gets around to give Free People the treatment, some of their units will find a home there.
Tomb Kings. While they looked cool, they were always a pain in the ass to collect. I never heard people raving about how great a kit the Screaming Ckull Catapult was. Or how well designed their bone horses were. People like the memes about Setra and the egyptian aesthetic. Another thing agains TK is, that they would play very identical to existing Death armies, so what's the point? If they ever do a new Death faction that's a redesign of TK, then it will need a lot ow work on models and rules, to differentiate them from existing armies and make them fit the AoS look.
Gitmobs are there, it's the Gitz. If you ever tought about WHFB and goblins, then Night Goblins weas what came to your mind. They were always the iconic part of the Goblin range, They have now their own identity and army.
Greenskinz are kinda in the same problem as TK and death armies, that game design wise they have no place. You have your lightly armoured orruks, the Boneplinterz, you have your more heavily armoured ones, that's the Ironjawz. If they would expand the Ironjawz, there they could make a comeback as light infantry, light cavalry, orruking warmachines or being ranged fighters. But as a seperate faction? Nope, not seeing it from a game design perspective.
Or again, they get a complete redesign.