It's more or less a matter of time until everything will be migrated to go. Since it has better performance and works good for them, there's no point not to do it.
I don't know about you but its hard to sell upper managers on complete rewrites of things when the end result is: no real change but it might/should/could run faster. Unless performance is a concern to be addressed the risk of changing technology stacks doesn't seem a great idea.