I like the idea. However there's already the campaign

I always thought you should have an arena option to fight your own mechs and/or your own buggies, tanks, towers, etc.

The way I see this being done the cleanest is to revamp the arena lobby. It would need a series of options like ladder, just for fun, 1 player, campaign, etc. It would also be nice to have 6-20 mechs in your garage and select them right before a battle (like pocket monster stadium) instead of having slot 1-3 always default in that order. Since campaign will be incorporated into this system, Chatting and Battle! can probably be separate buttons.

Then again, if the development team is going to revamp campaign (as they should), it might just as well wait for version 2 or 3.0.