For much, not for all.

System and user files are pretty close to one another in NixOS, so I use it for both. Sudoedit is set to vim, but I have a kitty and neovim (technically it's nnot nvim, it's nvf so I can config it in Nix instead of Lua) environment that tiles quite nicely and uses nonconflicting keymaps.

I use mod+hjkl for navigating my window manager, too, which has led to an interesting situation. Hyprland just migrated to Lua from Hyprscript, and Neovim uses a lot of Lua for inbuilt commands and stuff, so you'd think I'd be thrilled to write them both in the same language. Instead I just sigh at the greener grass because I already configured them both in Nix.

I do use Obsidian (with Vim binds, and monospace source mode as default for everything except tables) for my markdown viewer / primary notekeeping cloud sync, and Kate for previewing media that needs to be formatted right as a .doc or .pdf.

Some Obsidian notes are handled with Vim, actually. I have a script that sets up a new Zettelkasten note with automatic tags and opens it in Neovim, because I find it faster than Obsidian when I have a single thought and need to write it before it's forgotten. Thanks ADHD. I write Zettelkasten like little scripts of code - unique, atomic, referencing and importing each other, with a unique version history, and Vim's great at that.