Yeah, that doesn’t sound unreasonable at all. You need a ton of capital to start something like this.
MS won’t even give you the time of day unless you have everything planned out, the funding to make it happen, and of course, the money to cover legal fees to get the licensing agreement in place. And MS’ share won’t be peanuts. You’d likely be looking a per seat license fees of many thousands of dollar per year, plus potentially a percentage, much like they take 30% from the marketplace sellers.