Anybody remember TermKit[0]? This was my first thought when I saw "JS/HTML/CSS Terminal". It was built on WebKit (five years ago, before the everything-in-JS craze really began) and had a lot of really promising features like smart MIME-type support... and then development sort of stopped.
I'd love to see the concept revisited with present-day technologies and platforms.
There are several projects working on this!
The biggest is Black Screen, but I've also got one and seen some others.
- https://github.com/shockone/black-screen - https://github.com/CGamesPlay/hterminal - https://github.com/sedwards2009/extraterm