I've noticed on this forum and the Slitherine forum that there is concern about the porting in to FOG2. From what I have seen from the video play-throughs and what @loki100 indicated (he's a beta tester), battle porting appears to be a very simple process.
As loki100 suggests there are 2 independent developers (Byzantine for FOG2 and AGEOD for FOG Empires). They have the same publisher (Slitherine), but they are 2 independent developers and games. I think it is really cool that AGEOD was revolutionary enough (and Byzantine was interested and like minded) to build-in this option in the first place.
Is there possibly another concern?