Yes, possible. In my experience, usually the very capable type, who's happy staying a HOT (e.g. focusing on family).

For SEO1 CEP - relatively common (but definitely less than the majority), yes, but in my experience it's seldom the case that all of them are actively seeking higher appointment at the same time. Some are happy staying as HOT; some still feel they're not quite ready to make the leap. For those who end up feeling frustrated at the lack of opportunity within the school, applying out is a valid pathway.