At present in code we've situations where enrolment plugins manually interact with enrolment instances in the database.
This imposes some pretty strict limitations as follows:

• We can't change database structure, indexes, or keys for enrolment tables as we may break enrolment plugins
• We can't implement caching of enrolment instances because we need to be 100% sure that the cache does not become stale and all interaction needs to occur through an API (MDL-29594)
• We can't reliably log enrolment instance events.

All we need is a little bit of API that would channel enrolment instance interaction (crud) to unblock all of these.
Doing so would aid in pulling this segment of code up to the 21st century.