Thanks for your appreciation of the invite system improvements! 
I think I understand your request and it’s interesting. Can you tell me some more about your use case and what you are trying to achieve? Are you inviting a bunch of different kinds of people to your forum who you want to send to different parts of your forum that everyone has access to? Or are you inviting them to private categories? Or is everyone joining your site facing the same challenge of understanding where to start? Do you have some concrete examples you can share? What are people saying who are trying to join your community and participate in discussions?
Have you thought about simplifying your forum, by switching desktop category page style to Boxes with featured topics and display categories on the home page instead of latest? Or adding a banner with information that helps orient people?
Along the lines @Rhidian suggests, you could also write a topic for each of these different types of users with a brief introduction to the forum, maybe with some screenshots or even a video, and some links.