The changes to ManaFlow Band + Presence of mind.

I think being forced to build flat mana doesn't always seem like a first buy for champions who optimize better with other items. will there be any other changes to runes that allow some sort of mana sustain.

Presence of mind isn't a great option since your more likely to get takedowns "after" a fight is finished, making the need for mana at that point redundant.

and manaflow band requires you to use mana before you even get a chance at mana regen. and even if you get the sustain, it doesn't give enough mana back if you have a low mana pool to begin with.