Those growth points, and their associated market knowledge and budgetary constraints, would become perfect transition points into a friendlier architecture for the team... Plan for change, moreso than trying to plan against change.

Decomposing and fragmenting an established service into smaller clones of itself should be reasonably straightforward. In most languages with a component story (ie java), library reuse across microservices should make your service architecture orthogonal to your application logic. This kind of approach also eases a lot of pain of cross-service issues.