I think control can be developed.
In the beginning of therapy we had no control, but with a lot of T work, and by developing communication and co-consciousness we developed some control with some alters.
In the last few years I thought I had a good handle on control, but recent events have shown me I don't. Even with our front co-operative group switching can still happen.

I imagine it would be a lot harder to develop co-consciousness and cooperation when there are uncompromising conflicts involved (gender expression springs to mind here. )

Hmmmmm, edited to add: Control has always been an impossibility for any of our hosty persons who have tried to assert their dominance over the whole group by being the 'one and only'. Nuh-uh - that ain't gonna happen! too many other viewpoints for that kind of dictatorship! They have always been overthrown pretty quickly!!