Celtic Heroes

That would be pretty cool!
The live quest element appealed to me cause it would scale with the areas you're in as you level, but I could totally see it set up as a wave-by-wave survive/kill challenge.
(just occurred to me that full tanks/support druids would be penalized here. Not sure if the solution would be making the challenge depend upon class, or making it a group event (both sound a bit overcomplicated and tedious))

An easy suggestion would be to reset all skills and stats upon start of the challenge, then when you complete the challenge, everything gets reset again. That would allow anyone to participate, and even a chance to try out new builds with no worry!

Ooo I like this.
Make it a popup that asks if you want to (wouldn't want to have to every time i you were happy with your build), and just hit a button when you're ready.
(Slightly of-topic, but they should totally make PvP like this too: you and opponent get warped to an area, popup gives the option to alt/reb temporarily, both players hit "ready" when they've skilled up, they fight, skills reset upon completion. Make a betting option too where each participant place an equal amount, winner takes all.)