Probably not a huge team, but I guess the number of people involved has easily 3 digits, as MS needs to pay the developers, marketing people, manage the release

Probably not a huge team, but I guess the number of people involved has easily 3 digits, as MS needs to pay the developers, marketing people, manage the releases through Windows Updates, collect feedback, check compatibility etc. At the scale of MS a "major" Windows feature can't be cheap, even if it looks simple. Seriously, look at how difficult it is for them to port the old style control center or improve notepad.exe.