IMHO thing an MS Linux could really add for SME IT teams is.

1) An easy way to join a Windows domain. Being able to use AD user auth and Windows file sharing with AD groups that is as easy as it is on Windows server would remove a major scare factor for Windows admins trying Linux. I hope this could be implemented by contributing to SAMBA and being a wrapper for SAMBA rather than a reimplementation. I have had frustrating times with Linux unmounting Windows shares and having to reboot to get them to remount.

2) Training. MS have a well trodden path for learning to be an MS admin. Bringing it to Linux would surely help more people test-the-waters.