Multiplayer will draw in far more new users than solo play I think. I know they are focused heavily on getting the Multiplayer aspect working at the expense of solo racers. But the Multi still has lots of problems as well. Go over to the S397 forum and read the complaint message from a driver at the 24hr Le Mans race. They have much work to do. You might think you are being forgotten, or ignored, but in reality, it appears they don't have a large enough team to work on many of the broken solo racing issues until they finish the multi-player upgrades. Realize too, the UI, which is the core of all future updates is close to 2 years overdue. They can't proceed with much beyond new content until they get that dang-blasted UI re-worked.
I don't buy that multiplayer is the only way to bring more players in. A well polished offline experience could absolutely draw a ton of players in, especially since there are no real options in the sim market for an immersive offline experience.
For all the flak F1 games get they atleast deliver a well put together offline mode and most the userbase is almost always playing the offline career mode. Look at all the people begging for a simple custom championship mode for rF2. The sim racing market is craving a well put together immersive offline experience with a great driving experience. It would be nice if a developer went for that instead of trying to copy what iRacing is doing.