Although I have not seen it in writing I was told that jumping from one link operator to another would mean having to start again so I would assume you would have to start again if moving to mainline.
This sounds plausable as annual leave etc cannot be transferred. The case with the superscheme being that each was set up under a different group of trustees from the others (?)
That was the case for the existing scheme anyway but perhaps koruflexi will be different in this regard.