Thanks for the long post! Also agree with Kelly, feels great to see that we are actually working on most of the suggestions already 
Regards strengthening the sense of belonging and being responsable by having invitations, I also totally agree and had brought it up already as well. To elaborate a bit more on it here, to me this approach is technically implemented very well on the forum:
- When users reach Member trust level (see Understanding user trust levels), they can invite others to the forum.
- All invites are publicly visible, on both the profile of the inviting user and the invitee (actually on the invitee’s profile it’s generally visible; the invites a member sent out are only visible to other members)
- Inviting is rewarded with badges. By default, there is 3 badges on the forum on this:
- Promoter: invited another user
- Campaigner: invited 3 users that became basic users
- Champion: invited 5 users that became members
Overall the approach is not so essential right now on the forum. It’s also not much used, as one can see on the badge pages… But the way it is set up makes a lot of sense and imo indeed something we should look to implement and adjust on the platform. Could work very well if we establish a Connections section, as discussed in Does anyone really need Friends? (The feature).
If we’d connect it to the score, I think it makes most sense with regards to the “quality” of the invites. Say, whenver you invited someone who has then attained a certain score, it also reflects a bit on your score. Could get very complicated though… badges or some rewards seem already good to me!