We don't have any knowledge of whether move values will be rebalanced again and even if they are, whether Twister will still be any good.
Unless they give Twister absurdly high numbers I don't think it'll supersede Dragonite as a Dragon type attacker, on gym defence sure it's annoying but Crunch is more so, with it's higher damage, and even then it's not an issue because gyms are too easy to take down.
Though you did say you had an abundance of fast TMs, and even if Gen 3 were to be released, I doubt you'd need to use all your fast TMs immediately, so you shouldn't be too disappointed if you end up wasting a fast TM, they're not that difficult to get even if you just do 1 raid a day.