Lot of good suggestions here, but I feel like if you're looking for DoTs/other status ailments/status buffs I'd have to be Green Mage.
Geomancer sounds like a neat idea too, but Geos and their spells are tied into whatever whether is currently happening, and while you could technically cut out that caveat for an MMO I feel it really wouldn't feel like a Geomancer.
Green Mage would be a great addition to the "supportive" job types in FF14, seeing as both other supporting jobs are both physical ranged. Shell and Protect might be difficult to implement and keep balanced, but Tranq and Leap would be awesome to see-- instead of just a tiny damage increase like the Bard and Dancer offers, give us buffs that offer increased direct hit rate (Tranq) and increased movement/spell casting delay/auto attack delay (Leap). While DoTs might not "technically" fit Green Mage, they'd probably be easier to implement and balance compared to Blind, Sleep, and Oil. Plus, they use maces, and we don't have a combat job that uses maces yet.
A personal favorite I'd love to see though would be Spellblade from Tactics A2. Red Mages are awesome, but they focus more primarily on ranged spellcasting. I'd love to see a magical "caster" that engages primarily in melee combat. Finding a way to make Blood Price work (Spellblade uses health instead of mana when casting spells) would be fucking phenomenal, but I also recognize its impossible in an MMO setting.
