For me, being a “Character” of a faction has always been about ties to said faction, and not about being an actual member of it.
I’ve always considered Gazlowe a Horde character, long before BfA, cause he has ties to Horde characters and only Horde characters. He has no connections to Alliance, and never really does anything neutral like with their players. The fact he wasn’t an actual member of the Horde wasn’t a requirement for me, the bonds and ties he had is what made him that.
Tirion, however, I did consider a truly neutral character, since he did have some ties to both factions, through being a former Alliance member before being exiled, and for his bond with Eitrigg which is what got him exiled to begin with. He had ties to both, so he felt neutral.
When Thrall was the Earthen Ring figure head and was leading the fight against Deathwing, he was still a Horde character to me. Sure, he had some ties to the Alliance through Jaina, but those were heavily outweighed by his ties with the Horde.
Bolvar is an Alliance character to me regardless of him no longer being an official member. His home is Stormwind, his ties to the Wrynns, his familial connection through Taelia, are all Alliance. He has nothing tying him to the Horde at all.
Maybe if he had like Deathbringer Dranosh as his second in command, friend and confondant, I could see it, but as it is he has nothing tying him to the Horde. Long time Alliance players have a reason to care about him, but Horde only players don’t.
That said, I don’t want anyone to be a world character, even if it was going to be Vol’jin or Cairne or something.