The active users count for beta features would be more helpful if it was a count of how many users had enabled it across all wikis rather than per wiki.
to show usage on the local wiki only a tooltip could be used with the text:
"X,XXX users on $sitename"
How to handle users who've not enabled it across all sites
Ideally this would be connected with SUL in that enabling on one site counts as an active user, and would be reflected in the total count, however they would not count for the site specific count on sites they'd not enabled the beta feature.