apply overlay by re-importing nixpkgs

This feels like a very hacky solution - especially inside a flake.
However, other do the same so I guess it is ok:
https://github.com/edolstra/dwarffs/blob/a536d80ed446d5a442f6c7c9b12c662e48fe60ea/flake.nix#L41

flake.nix

@@ -3,13 +3,16 @@
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-20.09";
 
-  outputs = { self, nixpkgs }: {
-    overlay = import ./overlay.nix;
+  outputs = { self, nixpkgs }:
+    let
+      supportedSystems = [ "x86_64-linux" "i686-linux" "aarch64-linux" ];
+      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+      fixOverlay = system: import ./release.nix { nixpkgsPath = nixpkgs; inherit system; };
+    in {
+      overlay = import ./overlay.nix;
+  
+      packages = forAllSystems fixOverlay;
 
-    packages = let
-      # doesn't work because it doesn't update the packages used by callPackage
-      #fixOverlay = arch: let super = nixpkgs.legacyPackages.${arch}; x = self.overlay (super // x) super; in x;
-      fixOverlay = system: import ./release.nix { pkgs = nixpkgs.legacyPackages.${system}; inherit system; };
-    in { aarch64-linux = fixOverlay "aarch64-linux"; x86_64-linux = fixOverlay "x86_64-linux"; };
-  };
+      defaultPackage = forAllSystems (system: self.packages.${system}.espressif-esp32-tools);
+    };
 }

overlay.nix

@@ -45,6 +45,6 @@ self: super: {
     '';
   }) {};
 
-  cntr = self.callPackage ./cntr/cntr-aarch64.nix {};
+  cntr = self.callPackage ./cntr/cntr-aarch64.nix { cntr = super.cntr; };
   cntr-new = self.callPackage ./cntr/cntr-1.4.0.nix {};
 }

release.nix

@@ -28,8 +28,9 @@ in
 , crossBinaryCacheSystem ? if crossAarch64 then "aarch64-linux" else null
 , system ? builtins.currentSystem
 , extraArgs ? {}
+, nixpkgsPath ? <nixpkgs>   # only used if cross* arguments are not used
 , pkgs ? if crossSystem == null
-  then import <nixpkgs> ({ inherit system; } // (addOverlay overlay extraArgs))
+  then import nixpkgsPath ({ inherit system; } // (addOverlay overlay extraArgs))
   else mkPkgsCross crossSystem crossBinaryCacheSystem (addOverlay overlay extraArgs)
 }:
 pkgs.lib.attrsets.mapAttrs (name: _: pkgs."${name}") (overlay {} {}) // { inherit pkgs; }