Well, if we were only balancing around high elo on this patch, I would say buffs to his heal. It's really underwhelming and on a very long cd despite costing a lot of mana.
Long term, they really need to rework support itemization for Taric to shine. Taric, plainly put, lanes like crap. The champs that are good are champs that synergize well with sighstone and one of the gold items, and Taric just isn't on that list.
When Taric is really threatening, it's because he can get a nice catch early and get ahead. In those scenarios, though, ANY champion tends to do well, especially the ones that scale. The issue is that he doesn't have the tools to ride out a tough lane.
Specifically, I'm thinking of relic shield on that comment. It can be really tough, especially against a poke lane, to get your stacks used on that item. Taric's heal doesn't help him sustain hard enough to just take the poke, and going coin is awful rn just because coin is awful. Even if it wasn't awful for everyone, Taric's heal is too weak for him to really utilitze the mana that he gets from coin well.
If coin were buffed, we might see that sort of a Taric do okay in the current environment (especially if they would buff that heal a bit). But relic shield Taric has WAY more weaknesses than strengths, and that's why he's doing poorly at high elo. He's just too easily bullied by other champs.
are all picked more than he is, and 
has double his playrate at support. His mana costs are high, his heal is nonexistent, almost every champion can dash out of his e, and it feels so bad playing him unless you're against a team like 
because none of Taric's ability scale with MR, only armour. He's a super niche pick at best, and even when he's put against full AD team comps, put play him over other supports?
