Arguments for using mains
First of all, this was never a problem before, why now?
cRPG's main attraction is its persistency for me. You have a character with a certain build, playstyle and gear set. A huge part of the enjoyability is having so many unique players which are recognizable by their style and gear. I can see that others feel the same, as every nostalgia thread is filled with 'do you remember x, who was using y and was awesome with it?' If we were to have skip the funs there would be different names, probably different builds, armors and weapons, we will lose the cRPG feel. STF's would throw this awesomeness out of the window for the tiny difference in performance.
Which is actually really tiny because the captains are going to pick players that they know and can count on. Every single one of those players has played this mod for a considerable amount of time and has a loomed main weapon and maybe a loomed piece of armor or can be lvl 33. The difference the looms and levels bring is very minor compared to the differences in ping, mouses, mousepads and computers.
Then there is something Zotte pointed out but hasn't posted here. Playing without looms will make the class balance very different. Playing melee without looms just means a little less protection and damage output, however for ranged, there is a considerably bigger difference for playing without looms compared to looms. To me this is just a flaw in current class design as classes should get an equal advantage from looming, but that is not the case right now. Ranged classes, most notably archery, will be a lot less viable without looms then melee without looms. Distancing the tournament even more from the regular cRPG experience.
Also you saying this is a skillbased tournament (people with large e-peens, surprisingly). Skill is a very relative concept. To me skill is what you can do with your body and everything belonging to your body. To have a real skillbased tournament the only variable between contestants should be their body. If you only take a look at professional sports you can see that its not even the case. Equipment and preparation play a really big role, still people say professional sports are true tests of skill. Which is just not really true. I think in cRPG the looms and levels are very comparable to what happens in professional sports, so I'd say its easily acceptable.
Sorry if I nicked any other arguments from the discussion in our TS, it was just time to get a real discussion going here and I wanted to present a strong case for using mains.
Restrictions
There should be equipment restrictions as in the balance of items, price is a factor. For one tournament, probably without upkeep anyway, people can go all out price wise, which is not accounted for in the balance. Therefore there should be price restrictions to compensate for the lack of upkeep which could potentially unbalance the class balance.
Class restrictions should be there aswell, but only to prevent like all cav teams or all archer teams, I think they should be somewhat loose, so there is actually strategy in picking the right classes for a battle. As the teams will probably have substitutes with different classes, they might be able to adapt to other teams. So for example having 4 cav should be allowed, having 4 ranged should be allowed. Not both at the same time though, maybe a minimum amount of infantry would be cool.
I think there should be no limit for crushthrough and pikes, there are no limits for them either in regular battle and they have their counters. Although maybe with the more skilled environment and more teamplay that this tournament has compared to battle people will be more able to unleash the terrifying maximum potential of these weapons, there should be a limit. Not sure yet.