Once I'm able to get in, I'd LOVE to help make a pvp arena! I'm becoming fairly good at frame theory, and I think in a void age, the best way to perform large-scale construction would be to have an airship with a flat roof and let the builder(s) stand atop it.
Frames can move pretty massive things. I think the default limit is like 5,000 blocks? I don't know if the frame + cover is one block, or if the frame is one and the cover is another. But I've seen some fairly massive airships in the youtubes. It basically comes down to how much server drag you're willing to put up with, but a frame moves about every .7 seconds, and I figure if you put it on something like a 5 second timer, it'll be slower but give the server time to handle it all, and not require everyone to stop everything on the server to wait for the frames to move.
I think the void world should be eternal day, as well. It might pay to get some IC2 solars running and a mass fabricator, because something tells me that once the TNT fighting begins, it would be nice to have a way to generate blocks and armor for arena fights. That way people wouldn't freak as much about having their gear shredded. And the massfab can also create prizes for contestants as well.
But what fighting modes shall their be? There's traditional deathmatch, or could have it where you just drop the prize in the middle and whoever gets out alive gets to keep it. Teamplay and territory control might be fun, install some structures with different tools and machines in them, to make a real fort vs fort warfare. Might be fun to use the wireless redstone pvp stuff as well, like jammers and whatnot. And then of course, there's the capacity to layer the whole interior of the arena in obsidian or IC2 reinforced blocks, and hold airship fights.