Why is everyone so obsessed about arenas... the arena in oblivion was lame and arenas in general are lame. You 1) fight and 2) get money.. both of which you can do any time, anywhere and easily. And once you do it theres litte else to get from it.
NO ARENA DLC!
Well, that depends. If the npcs you fight are like the ebony warrior in strenght, and are not actual characters, heck yeah. Also, if you helped capturing certain enemies, like trolls, or even dragons if you've gone a little far on the MQ. Also enemies from DLCs if you've got them. That would be nice, a playground battlefield for those who play on console and want to make epic battles.