When I was a Switch, I found that the women I was attracted to as Tops were firmly in the Dominant category and I could not consider them ever changing (nor could they). Equally, those I approached as subs were definitely subs and were certainly less dominant than I am and again they would not change.

My personal opinion (based on years of observation) is that all humans (even vanilla ones) fall somewhere on a scale between submissive and dominant (the proportions being similar to a normal distribution if anyone knows what one of those is). Whether you are able to sub for someone or dom for them depends on where they are on that scale relative to you. So if they are more sub you dom them, more dom you sub for them. The main point of my theory is that EVERYONE is a switch because unless you are at the very extremes there is always going to be someone more dominant or submissive than you.

I've been in a number of relationships with switches (oddly mostly vanilla relationships with some bdsm play included) where we would oscillate between being submissive and dominant. In at least one case there was a rota This was mainly because neither of us were more dominant than the other and it showed because we could never decide who was in charge so we have to enforce it.