After reading the code a bit more I think the new UI code+ajax is abstracted in a way that breaks the original enrolment plugability and code separation
I think the UI+ajax related to manual enrolment should be in enrol/manual, the cohort enrol UI should be strictly in enrol/cohort - not in enrol/ directly.

At present if you uninstall manual or cohort plugin the UI will not work, if somebody wants to replace those plugins with custom code the UI may break too.

I think it would be great to allow other plugins to extend the "Enrolled users" page with custom ajax code

There is no time to do this in 2.0, but I think this should be a priority for 2.1......