Jols, I was talking about footpocket moulded for your foot, not just an option of diferent footpockets mounted on the fin. Anyway, thats still long long way ahead for me, but its possible to make footpocket completly custom, thats for shure!
In any other way - technollogy of making fins, that is not possible or is too expensive and takes too long to make it, so the only option left is different inserts either glued or removable...

...as much as I know about these things.