Actually it may be possible, as I have discussed with the staff Microsoft HAS been spending lots of time in our VOOM forums.
I have also mentioned this here publically a few times.
Also I have heard some things over the past few months how the Mpeg4 that will be used could be some special Microsoft Windows Media 10 version of it and not pure MPEG4.
So knowing these things I would not be so quick to call it a April Fools joke (although its timing is bad)
However I don't think they would call the service WinVOOM, I would expect it to be MS-VOOM or something like that.