I do not follow why attributes support is a seemingly low priority.
http://blogs.msdn.com/b/vcblog/archive/2011/09/12/10209291.aspx
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2761.pdf

http://social.msdn.microsoft.com/Forums/en-US/vcgeneral/thread/caeede2a-7a2c-410b-93b1-f5ec108765ad

Without attributes you can't have MEF and I guess ASP.NET MVC.

I don't have any ideas on it, but I wonder if COM would be easier if C++ had attributes. Why would you need to implement QueryInterface if a DLL exported attributes that declared what interfaces it supported and where they were located?