Secret Hideout Caves

Speculative idea.. what if there were a few new islands, say one or two per region, that had these huge waterfall covered caves boarding the ocean line that you could sail into. This would be like going through a portal. It would just bring your ship and crew to an isolated cave that had shops and cosmetics chests but no emissaries. Loot wouldn't carry through very similar to how portals work and say for a pirate legend, it could a "wake up" spot. Leaving the cave would drop you from a random cave entrance. Also just like portals.