The Bard bug is pretty powerful and coding extensive, so it might be a while before he returns to runeterra.
Essentially a bard with proper timing was able to freeze inner turrets as the outer turrets were destroyed, which caused the inner turrets to be intargetable by players.
I don't know how Riot codes their games, but just from my knowledge of game design, fixing this problem would require them to either entirely recode Bard's Ult's affect on turrets, something that could take a few days, or completely recode how turrets go from being intargetable to targetable, something that could also take a few days.
The complication is that you want the turret to become intargetable after the outer turret is destroyed but also after bard's ult expires.
it will likely be a little while before the bug is fixed, however I don't think they will be doing any hard changes to his kit, as those would likely go through the PBE first rather than just be tossed into a hotfix. Presently there is already a large number of number changes to Bard on the PBE, so we can expect him to be a little to a lot stronger on the next patch.