i think new mounts for healers and dps would be awesome make it like the new tank mounts achievements actively do dungeons, roulettes and extremes of current expansion
could make it like this
Healers - Battle Unicorn
Melee Dps - Battle Tyrannosaur
Ranged physical Dps - Battle Griffin
Ranged magical Dps - Angra Mainyu

Though with player distribution i doubt see dps mounts but given that by end of HW there was roughly the same amount of healers as there were tanks but tanks got new mount achievements and healers got nothing in SB i think healers deserve new mounts and need as much enticing as tanks do give them some love SE also for each healer getting unique mount;
Whm - Winged Lion
Sch - Big Lilly(Fairy)
Ast - Big Card