I see your logic, but charges will hurt the overall play experience. I don't think there's a singular ability in the game where charges improve the 'fun' factor of gameplay. Cooldown timers while boring, never outright prevent you from using something. Charges on the other hand are one and done assuming there is no recharge mechanic outside of using a shrine.I am not a fan that the Devs are making the trance dependent on ki. If they give it 5 charges like every other trance and it cost 50 ki to renew charges, well that is ok then. But I fear there are no charges initially and monks who are low level will fight to have that much ki prior to fights and high level monks have many other things to spend ki on. No other class or tree has to "provide" something for their first five charges.
For the sake of 'fun' it would be better to leave the trance reliant on monks building ki (something they will likely have in abundance with this revamp given the lack of uses for ki) and having to 'go without' for a small portion of a quest time, particularly at lower levels, than to tie another gameplay system into charges and forcing folks to play the use-it-or-lose it shrine game.