Re: "Although it is not unreasonable ..."
Yeah think the reason they were always reluctant to do this was a) people would see just how sh1t some of it is, b) a lot of it is still actively proprietary stuff - i.e. still used in Windows 10 (and carried over from NT4/2K in some cases).
Also, the only way most people's machines are patched is through the WU servers - how you would feed patches to the general public through some sort of open source approach would be dubious and rely on the users either actively seeking it, or applying a patch to look to a different source (and then the obvious problem of who would host that source).