I don't really see this as a big problem, tbh. Manly because the stage separation is only content-related and the original content for S3 will probably be "only" 1 new car and 1 new track.
S2-licensed users will still be able to drive on more than 90% of possible combos.
It is certainly possible that the devs have a private "release date" for the Test Patch and are working towards that date, e.g. having the biggest things ready and just working on small changes where they can guess how long they will take. IMO.