I'll weigh in on the proposed suggestions:
Backpack as a rare powerup: I've decided to add it as a bonus on a mid game level. Which level? I don't even know!
Make enemies stop picking up items: This is actually a little harder to do than it first looks, since it involves a re-write of the former and baron ai scripts. I'll have to get my hands on those scripts first before I'll be able to change them.
Score counter: The game already has a built in score counter system, although how it works is mysterious and most sources of score aren't tallied until the end of the game. It sounds like it would take a lot of code. I'll think about it.
Add AoI restrictions: Surprisingly, that's an easy one line toggle. Sure, it can be done.
Upgrade weapons even more: ... alright, I can do that, although I don't know in what ways I should improve them.
Stop >100% health decay: Also a one line change, and would probably be a fair change.
Keep suggestions coming! I'll post an update once I can change the AI scripts properly.