GMS doesn't open the test server often, mainly for our own custom content. We probably won't see it open for Cygnus.
KMS uses their test server as they make all of their content from scratch, they must test it. Every other version gets their content from KMS so it has already been tested in a sense.
It takes time to implement things, as well, if you add everything at once, people would get bored and demand even more.