Requests for comment/Reevaluate LocalisationUpdate extension

LocalisationUpdate has had its time?

Background
LocalisationUpdate comes from a time when MW deploys were far and few between, meaning l10n updates made into master of MediaWiki core, and various WMF extensions were deployed at most a few times a year. For the last few years (mostly since post SCAP rewrites), this hasn't been the case. Deploys of master of MediaWiki core and extensions happen on a weekly basis (bar when the deployment train is delayed due to special events and holidays).

Problem

 * LocalisationUpdate and Scap fight - LocalisationUpdate deploys updates, any subsequent scaps then override these changes until LocalisationUpdate runs again the following evening.
 * Deploys of code and Localisation Update happen at a time when not many people are around. There is the potential of staged but not-yet-deployed changes on WMF deployment servers being deployed unknowingly.
 * This is somewhat mitigated by the fact l10nupdate uses its own directory structure to work, not /srv/mediawiki-staging (but still, it's theoretically possible someone populates these directories)
 * Routinely breaks without anyone realizing or knowing how to fix
 * No one is responsible for the code, those who support it do not understand it
 * Legacy shell scripts, independent of Scap
 * Weird mix of www-data and l10nupdate owned files on various hosts. Makes cleanup of older branches more difficult

Proposal

 * Disable and completely remove LocalisationUpdate from all WMF wikis
 * Allow SWAT windows to do scap deploys of new/updated messages where these updates are required for events, or specific launch of a feature ahead of the general train deploy