I realize this is a really old post, but I agree that Sitepoint has an opportunity to link the experience between the two domains more seamlessly. Even something simple like enabling SSO between the two sites would be great.
When I can sign into Sitepoint Forums with my Google account, but need a separate user id/password for Learnable, I then wonder if I'm the odd duck because I'd like to synchronize my activity on both.
Plus, this could also open doors for forums to replace the discussion threads on courses, which we have already established isn't the best user experience.
Just thoughts for consideration. Cheers!