There are a number of services out there, as long as they are WMS-compliant. However it would be better to have something that is maintained as part of the fork effort. The reason that Elastic has its own map service is that the one that they used to point to had overnight changed its license and required registration. Literally 100s of 1000s of users had their map dashboards break instantly. To avoid this in the future they created and operated the Elastic Map Service.
Here are a few examples of alternatives to the Elastic Map Service that can be used today…
