TeXmacs's own interface is deeply customizable by the user via Scheme.
I think you can set it up to have vim keybindings---see experimental code at https://github.com/chxiaoxn/texmacs-vi-experiment and comments at http://forum.texmacs.cn/t/a-very-tiny-vim-in-texmacs/176 (I know that the lack of a block cursor has put off someone, but I did not find that comment in the brief search I did now).