> - Is there any issues with sharing the same config file with another package manager? Ie. `package.json`?

esy can install JS dependencies just fine but we are supporting plug'n'play installations only (see docs https://esy.sh/docs/en/node-compatibility.html for more info on that).

> - On a similar vein, why JSON, and not a config format that supports comments, like TOML?

Yeah, we thought of that but decided to use JSON for now as it's easy to publish esy projects to npm - you already have package.json ready for publish! We might add support for comments to package.json soon though.

> - Will it be able to do Coq projects as well? I've not had a great experience trying to use Opam with it, and had to resort to using submodules. D:

I think it's possible now (I only use it install Coq itself to work through Software Foundations) but I'm not sure about the details yet.

But considering that Coq ecosystem is moving to dune (the build system of choice in OCaml/Reason native ecosystem) and esy supports dune very well I think Coq is going to have a first class treatment soon in esy!

EDIT: re JS compat: you can esy.json instead of package.json and then esy will use it instead. That way you can use package.json with yarn/npm.