I have a few several ideas.
The first thing would be to sort out everything ahead of time with the people who will be showing up, and give them scummy backgrounds/motivations etc. Doesn't have to be complicated, but just a general idea so that we can get some cool conflicts happening. Anybody who just shows up later gets... something. At the very least the admins should message them so that they know what's going on. At the most a traitor/antag role.
Second idea would be to simply give everyone an antag role, with the idea being that everyone will roleplay to be as scummy as possible, so mass murder/destruction would be a no-no.
Third idea would be to designate several gang leaders at round start, and use admin witchery to give them goals or something. Basically an RP rev round with multiple revolutions going on at the same time.
Fourth would be to have cult/rev going on at the same time if possible, to simulate two gangs + security. The main problem being, of course, having different round types based on converting going on at the same time. They might not work nicely with each other.
I see two main problems with scumbag round:
First, getting the shuttle called. Obviously the shuttle will have to be called at some point, but it can't be too soon/late. A corrupt Head selling the service would be an idea, so long as the other heads would interfere. Having everyone swarm the computer might work too, or we could end on consensus or something. Oh, and a point to make: Nobody should have the "Nobody should escape on the shuttle" objective. It would ruin the feel of the thing, I think. Unless only one person had it, and needed to recruit people to enforce it. Hmm...
Secondly, the jobs in the illicit wing. How are we going to handle them? First come, first serve? Work it all out beforehand? How?
Personally I'd love to see 1/2, with 3 when things get dull. At the very least we should work out some basic backstory beforehand.