My conclusion is that computed columns aren't physically stored in the columnstore, even when it's a clustered columnstore that "includes all columns". This differs from rowstore indexes, which will physically include a key column, even when it's a nonpersisted computed column in the underlying table. So you cannot expect a query speedup from segment elimination, run-length compression, and the other columnstore goodness for computed columns. They have to be recalculated each time.

I would be interested to see some official docs from Microsoft confirming this, and whether some future version may improve matters.