I don't think I have any in this criteria, but when the mythical gym rework comes, I HOPE that I will be powering up some different mons because they are now gym relevant. My list:
Steelix - seriously, how awesome would it be if he was a great defender?
Lapras - really wish he was back
And all the old standbys that are close but not relevant: Poliwrath, Slowbro, Venasaur, Arcanine, blastoise, charizarz, muk, etc