@jaffathecake I am always in favour of giving the author as much control as possible when it comes to these kinds of things. People will come up with wacky (good and bad) use cases which might get thwarted by assumptions about how stuff should behave, which leads to weird and possibly a11y hostile hacks.
Therefor I am in favour of an attribute on <selectedoption> that allows to opt in to certain behaviours.
@sjorsrijsdam of the four options in the post, which would you want to make available via this attribute?