Nome, how do you feel about making Tear a constant charge time like RoA? Right now, it's only chargeable on a small subset of champions who have mana toggles or 2s CD spells, and if it was made possible for normal champion to charge it, it would charge superfast on those. There's also the issue of if it had a low cap to charge, then it would be harder to use the item evolutions properly.
Edit: After some discussion, the idea proposed is this:
Tear stays the same. Charge system yadayada.
Manamune and possibly Archangels have the charge system replaced with flat mana gain over time (however much makes sense). This means you need to sink gold for having reliable fast charge time on champs that can't charge it, so it's not totally broken "spend 700g to get free mana, 1400 more to get dumb damage whenever".