Using THREESCALE_CONFIG_FILE is very useful, especially for testing.
However, in on-premises version there is no possibility to pull this kind of JSON from the API manager. The closest workaround I've found is to pull the specs for different services separately, and merge them manually inside:

{"services": [ <conf1>, <conf2> ] }

This is not optimal. So it would be good to be able to have a new endpoint that would work like the deprecated /admin/api/nginx/spec.json.

It could be simple enough, and only allowing to specify the environment, and it could always take the latest version of each service, e.g.:

/admin/api/services/all/proxy/configs/{environment}.json

(although it is not very REST...)