it's kinda on the back burner right now as I'm waiting to see how well forge essentials does with updating to 1.5 (personally, I'm using a beta version), but I have a mod in the works that should allow you to do what you're asking. I had a really early primitive version available for download, but my web server got messed up and I haven't reuploaded it, plus it's just for 1.4.7 and it's REALLY primitive with several bits not working for land claiming. I guess I could look in to seeing how well the updated FE works and try to get it back working though if there's demand, but I'll have to check exactly how perms work standard in FE for block breaking versus using as I could have sworn it wasn't possible to make it so you could use blocks but not break them, but that shouldn't be that hard to change (just write new permissions.... yay.....) and they already have some PvP related blocking features in the latest version iirc. So, um, if you're willing to wait a couple weeks for me to get that code all back working for 1.5 and flesh out the perm system and some of the background systems more, I could probably provide a mod that does what you're asking. I wish I could get one faster, but I'm still in the process of learning some of the SQL stuff necessary to do it properly and I've got some other semi-related mods I'm working on and after having to rewrite the entire thing at least twice already, I'm hoping to get it 'right' from the code perspective while still having lots of commands to make it easy to use and understand and both of those are a bit time consuming.
In the mean time, I would say that you could just start and kinda wait for the battle if you can trust people to 'follow the rules' so to speak for your activity. I really wish I knew of a mod that easily did what you're asking, but it's kinda a blind spot in the forge mod world as historically a lot of that was handled by bukkit and there isn't much in the way of large scale social servers that run forge and would need something like that.