Bilgewater looks completely finished from looking at those old promotional images. These go as far back as pre-beta POTCO though so more than likely it was just a developer "playground" for testing. Also POTCO used a very different "loader" or parser for loading world data code back in 2008. If they ever wanted to release it they would have had to rewrite their worlddata which they probably decided against. PvP cove on the other hand is probably from a planned expansion of sorts for PvP that Disney never fully developed. These models were removed from the phase files eventually as they do not appear in phase files from the time of POTCO's closing. You can see
@Johnny Sea Slasher shows off PvP cove in a
Wikia post from 2013. As you may know there were tons of unreleased content present in the phase files, from partial Kraken models and animations, to unreleased weapons and islands.