Listen to the wording on this… Forced. Forced, like blizzard would be tyrannical for not allowing boosts lololol. The psychology of justifying something like boosts… it’s unbelievable really.
You should be able to boost any character who is kept on the progression server. The only exceptions they have mentioned are blood elves, draeni and any characters on the soon to be released CLassic only servers.
In the TBC deepdive they talk about boosts at around the 24:03 mark. The only limitations mentioned are belfs, draeni and they must be on the progression servers.