I'm a little stalled on that side project, in that I've figured out what I think will be a working script trigger, but I have yet to grok how to set up events to apply province modifiers based on it [which is needed to test it, and then to apply actual game effects].

If I've read the Jomini documentation correctly and drawn the correct inferences from the existing examples, which is open to question, I think the valid trigger would be:

exclave_or_sea_from_capital_trigger = {
this:holder.capital_barony = {save_scope_as = hometown}
NOT = {
this = is_connected_to = {max_naval_distance = 0 allow_one_county_land_gap = no target = hometown}
}
}

But events are just out of my scope (puns) at the moment and I don't have time to chase it down further.

Anyway, if that does turn out to work, it's free for anyone to use, attribution only if you really feel strongly about it because I'm not bothered either way, Cathedral ethos, all those good terms.