There will definitely be a new league for the game when it's released. The Killing Zone (www.tkz.net) was one of the more immersive gaming leagues for mechwarrior 2, mercenaries and mechwarrior 3. I'll be relaunching the site as gamerleague.com with a more advanced automation system. Probably won't be done until end of the year.
The ironic thing is I was getting so nostalgic that I rebought mechwarrior 4 just last week.