I would think as the top coaches continue to move up, it'll make D2 more appealing, because you won't have to get smashed by elite coaches repeatedly. Realistically what will also help is just educating newer players so they don't get overwhelmed. If you just start playing, and are in a D3 or D2 division with top coaches, you're gonna give up relatively quickly.
One idea to get even more people into Wilkinson, is if beginners view it as a good place to learn because you get a lot of advice and help. If beginner coaches knew they would get more help in Wilkinson than other worlds, they'd be more likely to join it I think. Maybe people could contribute towards a forum post called "Crash Course in WIS" or something, similar to what GD's Guide To the Game was, except for the current engine and a lot shorter. I'm talking about something that takes 5 minutes to read and 5 minutes to implement and makes it so you can beat a SIM every time basically. I think that's doable and would make D3 people enjoy the game more.