I want Fomoria to get underwater recruitables! Undead ones, and creepy fairy sea-monsters, like kelpies, morags, merrows, cecaelias, lavellans, and dobhar-chu.
All I am saying is that the logistics of invasion are vastly different if you cannot do PD at all.
I know you can give any nation PD before a game starts using the map editor. I wonder what would happen if you give a land nation a starting water province with PD... maybe nothing, but who knows.