How do I run the ecosystem the docker already has with nix alone?

It's not just the runtime.

I'm not certain what "ecosystem" means in this context, but you can build docker images using Nix. It's actually pretty cool because the image only contains the runtime dependencies of whatever you throw in the container. No package manager or build system is included. I've only tinkered with Nix, nothing in my professional life, so YMMV.

I'm super interested in the ecosystem you mean here. I'm assuming that you mean ecosystem around images like kubernetes, ECS, etc like the other commenter guessed?

If so, I think Nix being able to create docker images addresses that specific concern.

Can nix run images created with docker?

Yes.

See https://nix.dev/tutorials/building-and-running-docker-images

Or do you mean run as in "use docker image(s) within a nix expression". Like if you have a webapp with a nix devshell but want to start the docker postgres container for development?

You can do that too, yes.

I can easily install many apps hosted at the Docker hub but how would I achieve that without Docker hub, unless everyone starts hosting things elsewhere but that'll take a good while assuming the community's consensus is to ditch Docker altogether.

> I can easily install many apps hosted at the Docker hub but how would I achieve that without Docker hub,

I'm sorry, I don't understand what you mean.