[pjmlp]

Those exist since the 1990's, and sorry to say, they are hardly unknown.

[chungy]

Perhaps they aren't. TeXmacs is also from the 1990s and from your brief description, no compelling reason was offered to prefer them. :p

[pjmlp]

So here is one, plenty of people used those at CERN, I haven't ever seen TeXmacs in action.