I think I've noticed that I may have communicated something incorrectly, so let me clarify something about my original post and suggestion.

I didn't meant to imply that every cooldown can now overflow up to 50% of its cooldown. Rather, what I was suggest was that certain actions offer cooldown overflow just as certain actions offer charges. Some actions can offer charges while others offer overflow. How much the action can overflow can differ from one action to the next, and some actions will continue to have no charges or overflow.

I think the way I wrote it originally implied this was a system for every cooldown rather than an alternative option for certain actions. So Astrologian's Draw, for example, might feature some amount of overflow to both allow you to time your card draws and plays, but something like Bard's Bloodletter would still feature charges because of how Mage's Ballad operates.