Nice to see Galio getting a slight buff. This won't improve his abysmal play rate or really have an influence on his usefulness in games, though. No, to do that, he needs a change to his ultimate.
His R (Idol of Durand) needs changing. Before, QSS was the go-to item to counter Galio, and that was okay, because it ended up taking an item slot on your carry. Now, with it building into Mercurial Scimitar for the last three years, it's made that trade-off largely ineffectual and not even purpose-built.
* A person cannot remove the taunt debuff by means of QSS or Cleanse. At all.
* Cannot be interrupted.
This would simply be giving Galio a quality of life update that he really needs. It would certainly bring him back into the meta, after a very long time out. He doesn't need any number tweaks. The high mana costs are necessary to prevent him from spamming skills and completely stomping his lane (be it mid or bot) early game.
It's possible that this would overload his ultimate and cause a lack of counter play. If both changes are too much, perhaps the prevention of the debuff being removed could be left out. Or, Tenacity could have an effect on reducing the debuff's duration again. However, it's the ability to be interrupted that currently causes Galio's ultimate to have too much counter play. It doesn't even make sense! He turns into a statue. How are you supposed to distract a statue? I see no reason why, given how antiquated his kit is, his ultimate can't receive this buff.