This is indeed the proper way to do handle this, in my opinion. It is fine to release it first with a SFM to test the avionics and all the other stuff, but having to different flight models in the game would be bad.
VEAO said that not many people bought the SFM only Hawk version, most just bought the EFM version which has the upgrade included, even though it doesn't even have a release date currently.
Nobody wants to stay in the SFM plane.