The concepts I have in mind are in the list below,
- PreTrost based RP; mainly during the suicide run to take back Maria. Contains strategic values and a baseline story.
- Talons of Liberty RP; the stroy of the branch off of the survey corps. Mostly sandbox, other details to be set.
- Invention of the 3DMG; the first battles against titans with 3DMG, lots of swing and miss/discovery style story.
Also, for mechanics and rules to make it interesting and organized, I have a few ideas. It can be %100 player controlled, it can be like a text-based adventure game, or a mixture between. If we were doing 100% player conrolled, than it's colaboration storywriting, which puts a lot of trust in the RPer's writing skills. Posts should be long, but there can be confusion and conflicts in the story. For RPG style, it'd basically be like PnP style (dungeons and dragons) roleplayng, where the GM has values, players have stats, and most things are decided by a chance roll. Posts are small, and it takes a while to progress.
For the third option, we could do just a few stats/values or chance rolls that decide the outcome of complex actions, like killing titans or tricky manuevers, while doing most other things, like cheap shoting people in the butt, is just done by the players with their own self-defined failure rate. I'll probably make a character sheet to clearly define skills and weaknesses so people can do most things without GM involvement, that way stats are kept to a minimum.