In S4E2, you can play online, which means almost infinite goes with people: no issue there, especially since there's a few TSCers who are willing and able to play as well as the rest of TSC (or be able to learn, we're a generally intellectual bunch). I know a lot of people have lag and it's not at all a perfect system, but lots of people *could* get use from it that way, if limited to some extent.
In the rest, you'd have to play offline (does/can netplay work over LAN? I need to go look...), and I'm not specifically sure there's an advantage in all of the levels that have co-op... like in S2, there's no benefit to having Tails in EH1 in any category, I don't believe (maybe score?).
And while I'm only one person, I learned how to use Tails in S2/S3 for a handful of uses because I wanted to try and copy parts of the TAS. I can either dual-palm the controllers (A trait I'm not sure how many people have learned...), or in some cases play with my feet (if it's something like one-tap SD or just keeping tailed desynced)
Also, if it's a sub-site you wouldn't be required to play. It wouldn't have any base effect on TSC except the extra bandwidth (which I don't know that that's a problem, afaik our site runs plenty well).
I mean, I have a 2P (My gf), I have net, and I have the ability to play two characters in some instances, so I certainly stand as someone who could/would have full use of the site. Which is why I *don't* support it being on the main site: having someone to play with isn't something available to everyone, and it's far harder to get a decent, competent player than, say, to get DLC, and those already warrant separate games.
I don't even know if I'd really compete (I would probably upload my S4E2 stats I have with my gf, if for no other reason than that I have them), but I think having it open would be better, and unless it's a huge load on the site (which I don't know, both not being a networking expert and not knowing the site specifically), I don't see the problem with it, since SDM said "I'll do the charting" and "it won't be hard", from what I've seen.