Suggestions for a Taric rework

I like MOST of Taric . However, his passive is quite possibly one of the worst in the game, save the cooldown reduction. There are items that do it, and they do it better. Also, some other things. But first, the new passive!

Passive-Gemcraft-- Taric's damaging spells add a gem(other name?) mark to enemies. Basic attacks and spells from allies, and basic attacks from Taric will do 20% of his armor in magic damage. Also, if Taric attacks an enemy with the mark on them, his spells will decrease in cooldown by 2 seconds. This effect can only occur once per 5 seconds.

Personally, I think it would add some gameplay diversity to a very boring champion (save that one game where you get fed and become an unstoppable force) and make him more interesting to play as.

I think Riot shouldn't completely redo his looks, just improve it in places where it needs to be improved, and polish it up.

And make his ult a knockup, it just makes sense really.

Please tell me what you think, if you read this at all. Thanks!

EDIT 1- The "once per 5 seconds" refers to the cooldown reduction, not the entire passive.