upd

system/term.nix

@@ -1,3 +1,14 @@
-{...}: {
+{pkgs, ...}: {
+  programs.bash = {
+    interactiveShellInit = ''
+      if [[ $(${pkgs.procps}/bin/ps --no-header --pid=$PPID --format=comm) != "fish" && -z ''${BASH_EXECUTION_STRING} ]]
+      then
+        shopt -q login_shell && LOGIN_OPTION='--login' || LOGIN_OPTION=""
+        exec ${pkgs.fish}/bin/fish $LOGIN_OPTION
+      fi
+    '';
+  };
+
   programs.zsh.enable = true;
+  programs.fish.enable = true;
 }

system/users.nix

@@ -3,7 +3,8 @@
     isNormalUser = true;
     extraGroups = [ "wheel" "networkmanager" ];
     initialHashedPassword = "$6$Qab6SSvEJM2YRtVA$7Oyl7E3pp/FKtCC.2Tb2tyzp3yp7BFHFAKngUYJssQJ.v1Q2mqsgW9m7njpaKNcka2vyCwrnmw1R.YPlFqR0p1";
-    shell = pkgs.zsh;
+    # shell = pkgs.zsh;
+    shell = pkgs.fish;
     packages = with pkgs; [
     ];
   };