I think a super easy example for me is dark knight. However I do like tank dark knight and an authetic harming yourself dark knight in PvE would be a knightmare for healers. Reaper has a somewhat similiar vipe as in using shadowy magics but as dps. (Plus in XI the sycthe was a pretty good weapon for dark knight)
I also wouldn't mind seeing Astro as a dps. A gambler esque dps with cards (and probably dice). Fortune telling enemies doom? Something like that.
I think Monk or Samurai would be solid tanks. Gorsetsu tanking in trust duties is always a win.
I know nothing about it but Viper as tank because we don't need 2 new dps jobs >_>