I'm going to come off the bat and say that I've been PKing on Era since 2002, and I'm still not bored with it; so I'll have to harshly disagree with your introduction.
Gang activity, street PKing, and sparring is where its at.
I admit, gangs have fallen way off since 2006. Nowadays there's no real "gang loyalty" anymore. No working hard to ride the ranks, and no incentive to advance.
But the PKing is still there.
Provided that the players kept coming, I could sit in the PK Arena all day.
Adding new skills would change the dynamic of the game too drastically.
It simply wouldn't be Era anymore.
It would be alot like a 2D Battlefield Heroes
I do, however, think this would make for an interestingly unique event.
You gain points through playing, and you can chip them into different skillsets, with different levels. Similar to Laser Tag's upgrades on PC Era.
If it is exceedingly successful as an event, we could possibly implement it.
Nice well thought out idea.