I think the expelling is totally fine. Martin and his team put a lot of time into this, developing the course and the tools to automate grading and if someone is going to put this up publicly and not take it down they should just boot them from the course.
I don't understand why anyone would actually turn in the same work, though. It's not like a completion certificate from this class will get you closer to a degree or anything. I'm sure there must be some reason and I hope it's more than just "I wanted a 10/10 for me to see!". I suppose that an employer might tell someone "learn Scala and get that certificate and get a 10/10 on every assignment" but I somehow doubt it.
There it is, really obvious too.