I will confess, I was inspired from a multitude of sources (Gundam Wing, Code Gaess, Mechwarrior) and amalgamated them with a twist, one of those eureka moments on the porcelain throne.
Anywho, the way I see it, players will be PL 6-ish, maybe 8, having no powers save for those explainable by excelling in some ways (Speed 1 for great athletes, Senses: Rapid for speed readers sure; no eye beams) and PL 10 for the mechs.
The Mechs would be power arrays, really. They would have some implicit powers (a couple levels of Protection, Immunity to the rigors of space, such and the like) which would make them cheaper for players to tinker with, but I would give plenty of leeway for customization. Since it's a sport, you can imagine that having a wacky mech concept would be good and bad, and likely promoted.
I think the only limitations I would place would be No Magic, no Time Travel, and No Space travel. The latter being because a FTL engine is monsterously huge and impossible to fit in a mech. I'm on the fence about teleport, since it's not in the tech capabilities yet. If someone wants it, they'll have to sell me on the idea ahead of time.
Also, I'd restrict the size to be nothing larger than Size 1 (60 feet tall) which is still a respectable Growth Rank 12 so there really shouldn't be any complaints. Any larger and the mech couldn't be dropped by drop pods or ship-born launch systems, making it less a vehicle and more a structure.
As it stands, I'm highly considering throwing down an Ad within the next week or so, once I've gotten a little free time to work on NPC's and the like. I've not even named half of the Unjudged that players would be working with. XD