Anyone here heard of Skyfarer? It's a Fallen London/Sunless Skies/Sunless Seas RPG. Looks like it might work as a PbP, too.
I don't have any ideas for a story here, but maybe someone else will? Just posting this page with a link to the rulebook here in case anyone feels inspired by it.
(Sorry I couldn't post the direct link, but it's a script).