You can get the full expansions for free with a CD key of the original game on their website, I found out a while ago when I found SC1 at a thrift store.
[0]: http://www.teamliquid.net/forum/brood-war/520460-starcraft-v...
This bit is good to know. As usual Linux support will unlikely happen. You can guess from that as well that SC:R would lack macos support if they are not able to address the existing issues until its release.