I would like to see an option for new solutions or updated solutions being made available to ArcGIS Enterprise at the same time they are made available to ArcGIS Online. Then there could be checks to make sure the required functionality is available in the version of ArcGIS Enterprise that is making the request.
Surely a flag could be added to ArcGIS Enterprise to choose between using the cloud solution repository or using a locally installed solution repository. That way organizations that what to use the latest solutions can do so and those that want to be offline have the traditional local installer.