There is currently a proposal on Area51 called Ask Microsoft. Its questions, similar to Ask Different and Ask Ubuntu, would be exclusively about Microsoft. There was a discussion there that all not-off-topic-or-subjective questions would belong here. Is this true, or does the proposal have merit?
I think this is the discussion you referenced. Somebody said of that proposed site (excerpt, but a good summary):
I don't see how this could be different from Super User.
I can think of one big way in which Ask Microsoft would be different from Super User: non-desktop products. If the Ask Microsoft site really is about all Microsoft products, questions about Windows Phone, Xbox, and other Microsoft miscellanea could only go there, not here.
There might be a good deal of overlap between the two sites, but then a different culture could appear, like on the Unix & Linux site. Ask Microsoft isn't even close to private beta yet, so they haven't had a chance to figure out who they are. Once they get there, we'll see whether the proposal has merit.
You will get to see what others think, even if you disagree. In the end, Area 51 is a place to explore these ideas, flesh them out, see if they have enough support and if lucky make it to private Beta. Once there they will need to meet certain stats to be eligible for promotion, or not.
For instance there's a suggestion to merge it with MS Office proposal. Over on the office proposal, I asked a question. While I personally think it would be ridiculous for VBA to be in-scope at another site, the point of Area 51 is this type of discussion.