A quick search revealed very few options and those few were using paid software.
Do some searching yourself about conversions, Sweet Home 3D can't do it.

I actually did a lot of searching but can't find a single application or tool or script that could do it, so i'm hoping anyone has that holy grail somewhere.

The format for .fml seems to be a real standard see:
https://floorplanner.readme.io/referenc ... cification

So hopefully technically it's possible.