Sounds awesome.

Though I’m not sure of the solution really is / should be increased sandboxing.

The alternative may be a rethinking of the increasingly smaller packages. Maybe it’s better to have few large packages maintained by reputable organisations or personalities?

The problem is large, sprawling and complex. In an ideal case, we'd have high quality packages maintained by reputable people/organizations. But today this just isn't true. Open source takes contributions from a large number of unknown authors/contributors with motivations that may or might night align with your own.

We really need a defense in depth approach here. Sandbox where it makes sense, perform analysis of code being published, consider author reputation, etc.

Why is there so much discussion about sandboxing? Why wouldn't I put some malicious code in the package itself limiting myself to installation only?

A lot of the malware targeting developers is leveraging the installation hooks as the execution mechanism. So sandboxing the install helps stop this particular attack vector - which is why it gets talked about so much.

If you put code in the package itself, this would side step the "installation" sandbox. However we're also doing analysis of all packages introduced to the ecosystem to uncover things that are hiding in the packages themselves.

So you're right, we need a defense in depth approach here.

I think this is a very good idea. It should actually be built into the OS. I know of BSD jails, but not sure what else there is for Linux/Windows/MacOS.