A multiplatform league would be more than we could ever handle.
You have rF(2) and Le Mans. Switch to AC for Nords, then iRacing for Spa and even Bathurst, then LFS for Aston or new Westhill. It'd be way too difficult to have people with all the Sims and content in order to maintain the league.
Anyway, toward Ben and Thilo, a change had to be made, and iRacing was the only logical choice.