Why shouldn't this be upstreamed?
But looking at it from a perspective where Nixpkgs is the upstream: what does this introduce that would be unwelcome in Nixpkgs' bundlerEnv, or perhaps situated so it can share code with the existing implementations?
Trialing new designs in your own space is a pretty common pattern and there’s ample history of good ideas being adopted upstream once proven.
Or sometimes you just might not have the energy for it. It’s okay for your gift to the world to merely be available, without pressure to go farther.