TwitchTVJohnOur standard requirements are 300 + concurrent viewers
There are a handful of people who actually already fit this category assuming they actually keep streaming a good amount (aka banny and ruwin)
Subs would be an interesting thing to see for tf2, but as is if you just want to support your favorite streamers it seems like donating directly is a better idea. Unless there's custom smileys or sub only stuff that people start doing (like sub only pugs or something) then there's little incentive to actually sub to someone other than out of the kindness of your heart. Not that that's necessarily bad or anything, but at least for diablo streams and things like that the streamers will do sub only events (giveaways, sub only boss runs, stuff like that), so it would be a good idea to think of something analogous in tf2 before you went ahead and invested the resources in it.