Well rumour has it that 7.5 is due out next monthish. Hopefully all that documentation that is appearing is a good sign.
Looking at the latest support matrix ( http://www.symantec.com/docs/HOWTO9965 ) Windows 8 appears to be supported by CMS 7.5 but 8.1 is not. This isn't surprising though as 8.1 seems to be a cosmetic change that Microsoft have kept close to their chest until the last moment. It seems like a reasonable bet that even if its not immediately officially supported that it will behavve the same as W8. It would be great if someone has tested CMS 7.5 beta 3 against W8.1 could add a comment?
Server 2012 appears to be supported by SMS 7.5.
I notice also that W8 is shown as limited support by 7.1 MP1 but 2012 is not supported.
Windows 8 and Server 2012 are not supported as a site server (probably related to the IIS version they run?).
{Edited to make more sense}