I'm going to throw a few wild ideas out there for possible features.
Weighted Scoring
A scoring system which allows the trust level to be created based on a numeric score that is calculated by assigning a value to each enabled metric. This could allow weighing certain metrics more than others depending on what the trust level is for while still allowing each to count towards the same trust level (e.g. 5 points for each best answer, 2 points per like received, 1 point per post). If implemented there would be two options for trust level criteria, the current per metric value/ranges or a total score (sum of all enabled metrics scores).
User Rep
This calculated score above per user could even be displayed as "Rep" (or some user chosen string) on the users profile. A user could see their rep, and if the scoring criteria was published by an admin (e.g. 100 rep for trust level 1, 200 rep for trust level 2), then a user would see their progress to the next trust level. If they have no information on what the thresholds were for the trust levels they'd still have a cool Rep score to look at and perhaps encourage them to keep doing well in their community. Perhaps a permission control for who can view this on a users profile (admin, only self, all members..)
Give Rep (Achievements/Awards)
Admins could reward users with more rep/points based on actions possibly not tracked by any forum metrics. Perhaps they made some excellent PR's or provided outstanding support to some users on discord so you decide to give them 100 points/rep. Now this one, I am not sure if it would fit into this extension or may even be a better fit for a separate extension (like an Achievement or Award extension) that trust level could just hook into like any of the other metrics and fetch the achievement count or total points given for all. If it were a separate extension, when an achievement/award is given the user could get some cool badge with an assigned value of points which are all visible from their profile under an awards/achievements tab. However, now that I typed this out I am thinking it would be kind of cool to get achievements automatically as well based on different criteria where you could define these milestones (e.g. first post, 100 posts, 1000 posts, or any of the supported metrics) but that is also something that trust levels already has the smarts and logic to be able to do. Maybe this trust levels extension could offer both features (group assignment & achievements) through a toggle which sets the criteria to be for a group assignment or achievement, or maybe this extension can be forked and also serve as an achievement extension 😃 ??
It would be nice to be able to export all of these metrics of users or view in a table so one could easily see who has the most rep, posts, logins, likes, best answers etc. If I had access to that I could actually take a snapshot at the first of the month, see who had the most likes, or best answers in a month and give an award that provides rep. I am sure people would find other ways to make use of that data. This may also be outside the scope of this extension, perhaps a better fit for an expanded user directory extension or a completely new one.