It'd be great to create a twitter bootstrap version of this so you're not reinventing the wheel with CSS and allow for preprocessing.
I don't see why it couldn't be adapted for the default bootstrap grid, at least. What do you think would be involved?
I think abstracting the grid system, separating that logic from the editor, would be ideal.
I suppose plugins for different grid systems, including the built in one, would be the way to go, to stay in the same mindset as django-cms.
This way you'd be covered when twitter-bootstrap is replaced by google-bootstrap or some other flavour of the day.