T135027: MASTER_POS_WAIT() alternative that works cross-DC implemented cross-dc support for MariaDB. It would be important to have the same kind of support for MySQL 5.6/5.7 GTID implementation. While MySQL it not currently used on production, this would be a blocker for it, and a partial or full migration to MySQL in the future is not discarded.
Mediawiki may require 5.6/5.7 in the future (T161232: Bump MediaWiki's minimum supported MySQL Version to 5.5.8), and this would be how it supports those versions, together with T108255: Enable MariaDB/MySQL's Strict Mode.
This task should be relatively trivial to implement (GTID on mysql and mariadb work very similarly from the programmer's perspective), the complex part is testing it.