I switched to kakoune from vim in early 2020, and I really like it (previously: emacs 1994-2004, vim 2004-2020). It's worth prefacing what follows by saying that I heavily relied on the visual selection features in vim.

kakoune provides a limited orthogonal toolset that composes extremely well. After a week using kakoune I felt at least as confident with its command language as I did with vim's after years of use. Aside from a few vim plugins that were super helpful, I didn't miss anything after transitioning, except for the 'R' command (and to a lesser extent proper integration between the 'r' and '.' commands).

I worried that kakoune's multiple selection paradigm wouldn't scale well, that it wouldn't be routinely useful, etc. On the contrary, I use multiple selections heavily, often as a more ergonomic alternative to recorded macros, constantly for rectangle-based operations (whether multi-line editing, indenting, ASCII art creation, whatever).

Oh, for you tmux lovers out there, kakoune integrates amazingly well. All of its multi-window functionality directly uses tmux panes, with a server application (think emacs-server) tying everything together.

In terms of ecosystem, vim is much richer. But kakoune is a practical, beautifully designed tool.