I just had a call with MongoDB sales yesterday, and specifically asked if the licence changes impacts us, where we use Mongo as a datastore for our application, but we're not offering Mongo itself as a service. They were very quick and clear to say that the change is about those providers offering Mongo itself as a service. Using mongo in your stack to provide your service is not implicated at all.

The only grey area I see is if you offered some sort of database-as-a-service backed by Mongo but not explicitly sold as Mongo-as-a-service.