The arena idea sounds nice, hopefully it will be a big arena so it's not just a pile of people swinging swords.
Putting the nether as PVP isn't the greatest idea in my opinion, it's dangerous enough and it'd be more like whoever gets out of the way of ghasts would win, as well with the new stuff in 1.9 there will be more reason for people to be in the nether, the nether is a challenge already, sorta. We don't want a couple of people who have just mined heaps with diamond and low ping to just kill everyone and take all the new content for themselves.
