HN user
You wouldn't necessarily be "writing in your layout". You could do something where you have a separate preview pane that updates in real time. Similar to what Apple showed earlier this year with their Swift playground IDE, only for typesetting.
Great question. I've been wondering why nobody (AFAIK) has done this. Seems like the only worthwile reason to do something as silly as rewriting TeX.
Huh? As a European living in the US, I've had the opposite impression. I've never been to another place where every restaurant will automatically give me a free glass of water (and continuously refills it) without me even asking for it. I've also never gotten a dirty look for sticking with just water.
In Europe, you generally have to pay for bottled water, unless you specifically ask for tap water (and get a dirty look in response).