I can't see Mattel making a vintage-styled Crystal Castle because it was basically a doll house. Which works out fine, since I don't want a vintage-style Crystal Castle.
If they make a Filmation-style Crystal Castle, though, it wouldn't really be a playset by virtue of the fact that it's much taller than it is wide. Nothing would fit inside.
I think this Castle Greyskull thing is a one-time deal. It's the one playset they feel fans will completely support, so even if it's a huge success, I doubt it will convince them to try a CC. Sadly.