Nice question and good explanation.

But one niggle - either the explanation is wrong about NONCLUSTERED being a mandatory keyword for CREATE COLUMNSTORE INDEX, of BoL (the page you reference in the explanation) is wrong about it being an optional keyword - it's shown in option brackets in the BNF description of the statement syntax, so that it appears that although the index must be nonclustered it isn't neccessary to supply the keyword. I don't have SQL 2012 handy so can't check whether this is a BoL error or not.