This task cannot be completed till the day we migrate to gerrit 2.14. Low priority.
But we need to create a patch that at least does this, as Velocity templates are deprecated, per gerrit's 2.14 release notes https://www.gerritcodereview.com/releases/2.14.md#Emails
I doint know what type of warnings they will generate in the logs. It's best to convert instead of seeing a ton of Deperecated in the logs.