I agree with you that releasing it under the MS-PL licence would be
ideal.
It's possible they're nervous that if they don't keep type control
over it then mutant varieties will appear that don't conform with the
latest version of the spec - more likely it's just that their first
priority is to get something out there and they haven't given a lot of
thought to the non-Windows world.
From the first version I looked at (and logic also suggests this would
be the case) the OOXML SDK has a dependency on System.IO.Packaging
(from .NET 3.0), for the OPC stuff. Has that been implemented for Mono
yet? It doesn't look like it would be *too* much work, but that's easy
for me to say of course since I wouldn't be doing it and don't have to
juggle all the other priorities.
Have you tried contacting Eric White about this? (I don't have an
email address, but you could try
http://blogs.msdn.com/ericwhite/contact.aspx).
Getting the SDK in the hands of Linux programmers seems like a good
way to promote the format, and also combat some of the FUD that's
floating around.