1) We have [[ https://meta.m.wikimedia.org/wiki/Schema:MobileOptionsTracking | Schema:MobileOptionsTracking ]]. This tracks activity to the beta field (e.g. opt-in and opt-out) and lives inside [[ https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/master/includes/specials/SpecialMobileOptions.php | Special:MobileOptions ]]. It uses server side event logging.
2) We also log opt ins to beta/stable via wfIncrStats (statsd) for `mobile.opt_in_cookie_set` and `mobile.opt_in_cookie_unset`. It lives inside [[ https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/master/includes/MobileContext.php | MobileContext ]]
3) When a user is logged in and opts into beta we record this. This event is logged in preferences (https://phabricator.wikimedia.org/T67079#3815127)
Which of these do we actually need? What can be removed.
= Strawman acceptance criteria
 I propose we emove all code relating to #1 and decommission the MobileOptionsTracking schema. We will rely on statsd from now on.
== Questions we would like to answer
 changes in current (and historical) number of users in the beta feature over time
[x] ratio of pageviews to beta users over time
Done in T182235#3833724.