move all output modules to subdirectory, trash standard.nix

standard.nix isn't, is the essence here. Not all devices
support flashimage as it is currently defined - some
have diskimage, some have neither

modules/outputs/ubifs.nix

@@ -0,0 +1,48 @@
+{
+  config
+, pkgs
+, lib
+, ...
+}:
+let
+  inherit (lib) mkIf mkOption types;
+  o = config.system.outputs;
+in
+{
+  imports = [
+    ./initramfs.nix
+  ];
+  options.hardware.ubi = {
+    minIOSize = mkOption { type = types.str; };
+    eraseBlockSize = mkOption { type = types.str; }; # LEB
+    maxLEBcount = mkOption { type = types.str; }; # LEB
+  };
+
+  config = mkIf (config.rootfsType == "ubifs") {
+    kernel.config = {
+      MTD_UBI="y";
+      UBIFS_FS = "y";
+      UBIFS_FS_SECURITY = "n";
+    };
+    boot.initramfs.enable = true;
+    system.outputs = {
+      systemConfiguration =
+        pkgs.systemconfig config.filesystem.contents;
+      rootfs =
+        let
+          inherit (pkgs.pkgsBuildBuild) runCommand mtdutils;
+          cfg = config.hardware.ubi;
+        in runCommand "mkfs.ubifs" {
+          depsBuildBuild = [ mtdutils ];
+        } ''
+          mkdir tmp
+          cp -a ${o.rootfsFiles} tmp
+          ${if config.boot.loader.extlinux.enable
+            then "(cd tmp && ln -s ${o.extlinux} boot)"
+            else ""
+           }
+          mkfs.ubifs -x favor_lzo -c ${cfg.maxLEBcount} -m ${cfg.minIOSize} -e ${cfg.eraseBlockSize}  -y -r tmp --output $out  --squash-uids -o $out
+        '';
+    };
+  };
+}