The idea is pretty cool, but I'm unsure of the mix of TUI and animation. Once you start going down the path of animations, layout, fonts, etc, you start just reinventing the web - but with extra steps.

Personally I would cut complex animations (i.e. sub-character) and only have a single size monospace font. I would rip out CSS and go for maximum compatibility. (If something exists like that, please let me know!)

Another feature that could be cool is to have this served (optionally) via telnet. I would also make it be able to produce static content (with a subset of features).

Re the telnet idea:

You might enjoy various https://charm.sh/ apps, especially https://github.com/charmbracelet/wish. They seem to prefer SSH to telnet though.