IMHO this is 100% the plan. If they play their cards right they stand to take out two birds with one stone (heh). They’ve already paid celebrities to be on there.
Still, this can only happen if Threads gets massive enough relative to the rest of the fediverse that the incompatibility doesn’t hurt them equally.
…that is to say, it’s all pretty likely, unless other strong competitors show up with ActivityPub support.