I am for anything that creates more sales and gives players more reason to log in.
I have long suggested that Arenas already exist, in the form of the training areas. Incursion is a perfect example of an Arena, just with AI only.
I think FD can develop Arena play to satisfy more gamers and make more money without too much effort. All the assets exist already whether ships, weapons or play area (stellar forge). They have already created training instances separate from the persistent galaxy, and 1.2 Beta just tested moving over account data like Credit Balance and Ships between different game instances.
This in turn leads to further development of the game, which is their stated intention and which everyone here should be very much in favor of.
Because FD didn't follow CIG into ever-expanding stretch goals and selling ships and getting $80 million, my greatest fear for the game has always been limited appeal (flight simulators), limited budget, and lack of fully deserved support. The game engine has legs and FD know Procedural Generation, but they have to have support or it will mean nothing.
So count me very excited by this and XBOX announcements. More players and more income is positive for all of us, even if they have to spend a small amount on a couple of new modes that utilize everything already built.
And as an example, the "racing game" that CIG made after arena commander took two developers less than a month start to finish.