Another modder is working on a script that might allow the game to understand blender models. They have already sent me a prototype which I'm going to help him with once I have a bit of time.

So that's not a guarantee, but there is potential in the future. :)

And even if it does happen, it won't be super streamlined: you would have to first import your fbx into the Unity game engine (which is free for non-commercial purposes, and generally quite easy to pick up) and then use that prototype tool to convert the mesh into something Megaquarium can understand. Basically, instead of having the game try to understand every mesh format, we would let Unity deal with it. The added bonus is that because Unity is a full game engine, we could use the mesh tool to preview animations, fix random issues like missing normals, etc.