The editor will not allow us that, I fear. There is no PvP mechanic or system atm and nothing which makes a "real" PvP mode feasible with the editor (rosters, ladders, official arenas, match-making, balancing, ....)
And not everyone will use Steam (and Steamworks) and - I say it again - many people don't use mods at all.
I really don't think so, does anybody in their right mind play an unmodded Skyrim? (please seek help if you do

)
And it will be almost impossible to fight against "stranger teams" in 2v2 or 3v3 because there has to be complete data-match. So every player would have to have the exact same game version and exact the same mods installed. Wow! That won't work. That will NEVER work. The only way to do this properly to include it in the vanilla version. Then it's like: "oh, I want to play PvP now, I just disable all my mods and swuuush, I'm ready!" That would probably work.
I like all the modding, really, but modding AND co-op are two principles that don't really work together well. That might work if you only play with friends (then you can manually communicate until both have the exact same version) but it will NEVER work with strangers.
IMO the mods VS co-op problem is even one of the biggest challenges I see for Larian (besides the combat AI and balancing). I'm curious how that will work out....
Well, if Raze is right this part is a solved problem already, I am guessing the "host" decides which mods are allowed and the rest just gets them pushed to them when they join. (really, it worked great in UT and that was 12 years ago...)
After seeing that last video about the editor I do wonder how it's going to work once multiple games have been released using the same toolset, even though you could conceivably get all the plugins without buying successive games (ignoring that I don't see why you wouldn't if you enjoy them) I assume you'll still need all the campaigns for access to the art assets.
Btw is Larian using this *toolset* (I know the engine is the same) to make Dragon Commander? Because if so that would mean there already *is* pvp and multiplayer support...and support for entirely different playstyles than the real time + TB combat of D:OS? I mean, that would be so goddamn awesome it couldn't even fit on any scale of awesomeness.
Still I'm edging more and more towards supporting putting full PvP support in the editor, though I still have my reservations about a default arena mode. I guess here we mainly disagree about the capability and creativity of the modder community...