We have them in kitchens that need to serve a large number of people - big offices, big hotel breakfast areas, transport lounges, etc.
But a standard kitchen, I think it's like someone else said in this thread: The time it takes to boil a 240V kettle isn't much more than the time it takes to get the mug ready, so there's no real benefit to going through the extra structural work to fit a boiling water tap.
Also I think most "boiling water" taps are actually like 95°C, not boiling, so if you're a black tea snob that isn't acceptable.
Is a peacoat a coat soaked in pee?