This one isn't much different from the perspective of someone wanting to expand to another field. You need a bachelor's in CS from an accredited 4-year program to enroll, or else you have to go through the usual placement-testing/remedial-course process if your degree is in a different field, as with the regular Georgia Tech CS Masters.

I don't see MOOCs as offering anything in particular that would make it easier to lift that kind of requiement. Large courses (whether in person or online) rely on incoming students coming from a standardized background, to allow the courses to assume a lot of things and minimize tailoring to individual students' varying needs. And MOOCs by their structure rely on instruction in (very) large courses.