If you can give it a try with AutoCAD 2013, it will work smoothly on Windows 8. I tested Visual Studio 2012 can create a plug-ins in .NET 4.5 that runs well on AutoCAD 2013 (in Windows 8). Of course .NET 4.0 is recommended, but 4.5 still works though.
You can do the same test from the attachment, but reference AutoCAD 2012 DLL files, see how it works on VS 2012, .NET 4.5 and Windows 8.
Autodesk saying something is 'not supported' doesn't mean it won't work for you on that OS. It means we've either not run our full set of test suites for that configuration, or (if we have) those tests revealed some problems. So its up to you if you want to take the risk. (For personal experimentation and testing, the risk is probably acceptable. For a production system your company relies on - that's up to you, but I wouldn't do it :-)).