Simply put I want to be able to manage the trust levels myself. Especially who can edit wiki articles.
Is this even feasible in the “open” system?
I need something like:
new users - can post in application forum only
once approved:
regular users - can post in several areas + can be invited to SIG special interest groups on the forum
execs - basically just another SIG + some moderator access
admins - full moderators (usually a subset of the execs)
Doable? 
I think you can do most of that, just create those groups yourself and set settings per category.
Meaning TL1, TL2, etc? Are you saying remove existing TL groups and re-create them and define them per my tastes? Sorry. I’ve only puttered around with the system very briefly. It’s rather sexy but I don’t have a deep understanding of it yet.
thanks for the reply! 
No, you can’t remove those. But you can set their requirements high enough to never kick in. And then you create groups like new users, regular users, execs, admins.
Thing is, you’ll then have to put every single user manually in said groups. For now there is no way - apart from creating a plugin - to have users automatically join a group apart from the trust levels.
If you were to create a plugin, you might want to think about attaching batches to groups, anyone working on that yet?
Ok that sounds reasonable. What limits would you recommend?
I had planned on using external ruby scripts to auto-assign groups for the bulk of users. The groups can be based off titles in an external source and pulled via API. Should not be too difficult!