I can't tell you what a relief this is! If GT6 were slated for the PS4, it would've split the league into two segments (GT5 players on PS3 and GT6 players on PS4) and that would be an absolute nightmare in terms of logistics and organization.
But now that we can play the latest and greatest Gran Turismo edition without having to fork out hundreds of dollars for a PS4, I imagine that the league will quickly transition to GT6 within days of its launch.
And then when GT7 comes out (holiday 2023? j/k), the PS4 will be much cheaper and already owned by many. At that point, it'll make the league's transition to GT7 fairly easy as well..
LONG LIVE S.N.A.I.L.