Allow more infusions on higher tier gear.

I think you should allow the player to put more infusions on higher tier gear items, in the same way it is currently possible with spells.

So 1 infusion for grey items, 2 for green, 3 for blue and so on.

It would add another layer to the "getting more powerful as i progress" vibe which is one of the game's strongest hooks for me personally (and i'm assuming i'm not alone in that).

If there is a concern about players getting overpowered, you could always gate the extra infusion slots by making them unlockable only for large amounts of essence, or with rare materials/crafted items.

Personally i don't see being overpowered as a problem though, it just means the game should spawn more enemies for the player to mow down! For me, getting OP is a fun reward for all that grinding. I mean, the goal is to become a god right? :D