A personal opinion after many years racing and representing International Formula Windsurfing Class.

Now the class has, in its rules, a fin and a foil division. Everybody can read the class rules.

At C.2.4 EQUIPMENT DIVISION says expressly:
(a) Fin Division

(b) Foil Division  [more]

Rule C6 explains the hull appendage in case of fin and foil division
C.6 HULL APPENDAGES C.6.1 FIN DIVISION C.6.1.1 LIMITATIONS

a) During an event a maximum of three fins shall be registered and used during an event except when a fin has been lost or accidentally damaged beyond repair. A replacement may be made only with the approval of the Technical Committee. The Technical Committee shall then attach an event limitation mark to the replacement fin and remove or deface any event limitation mark attached to the replaced fin. FWC Class Rules Page 8/8 1 st February 2018 (b) The distance between any point of a fin to its closest point to the hull shall not exceed 700mm. (c) Any other hull appendage other than the fin is prohibited. 
C.6.2 FOIL DIVISION C.6.2.1 LIMITATIONS (a) During an event a maximum of one foil shall be registered and used during an event except when a foil has been lost or accidentally damaged beyond repair. A replacement may be made only with the approval of the Technical Committee. The Technical Committee shall then attach an event limitation mark to the replacement foil and remove or deface any event limitation mark attached to the replaced foil. (b) Any other hull appendage other than the foil is prohibited.
It is simple, really.
After many tests, we can say that a FW board is the best board for foil boardsailing races.
Therefore, it has been natural to permit to FW lovers to compete with their favourite board in a foil division, and attract new sailors to FW races, proposing them a new way to play Formula windsurfing.  
I read on social media opinions about an alleged challenge between FW fin division and FW foil division. I also read of proposals, some interesting, to make the two divisions coexist, relegating them to specific wind limits.
Personally, I think that every FW sailor has the right to sail in the division he prefer and every division has to race in all the wind ranges. 
Many FW fin experts have the right to love the class in its traditional expression, because – perhaps like me – they love contact with the surface of the water and consider it an unavoidable component of our sport.
Others in the same way must be free to embark on the new challenge that the class has accepted to face, flying and experiencing a phase of technical development that will not be simple and not even brief.
A third group, having time to train and to trim, should love to challenge in both divisions. 
Nobody of us has the right to say what the best option is.

IFWC must allow all Formula lovers to compete in all these different ways, receive, and evaluate proposals from local organizers for a single division or both. The competitors’ interest will tell us which division will enjoy the greatest following in the near future.

I can say, but it is a personal feeling, the fin division represents in windsurfing what STAR represents in sailing. 
A class that, even if it is not futuristic, is credited with the greatest charm and appreciation of the best actors on the scene.  If today we want to make grow again Fin division, is the obligation of everyone to propose events of interest also for top riders, which can induce the youngest to recognize themselves in this way of navigating.

best regards, Francesco