Was considering why not just make ocean keep on going but instead of anything much being out there it would be just end of the map and your boat would start taking in holes like in Sea of Thieves, slowly or breaking down fast depending on how far out of bounds you go? Or shadows or special monsters that are part of the constant of sorts would not allow you to pass to escape. In that way there would be possible to make new secret islands of sorts in the outer bounds without needing to suffer the minimal amount of space that there's left in the current DST ocean!
I don't know if it's a big limitation that you can't build or do anything outside the bounds, or to have any kind of tile or turf where it all ends. At least in future update you could make the sea bigger, formidable and more adventurous. Right now it's all just a big fat lake with monkey pests around and moon tissue floating about.