1. near-universal adoption
2. "just works" experience: i.e. I can clone any random git repo, and run `npm start|build|whatever` and it's always going to work, without having to know anything about my environment or fiddling with configurations.
Does poetry do that?
From my experience, with repos that have Poetry set up, I do get a "it just works" experience that I've previously been lacking when working with python. AFAIK there is no "scripts" section (for e.g. "poetry start" like "npm start") in the config file, or at least no one is using them. You'll have to take a quick peek into the README, but the same is true for npm projects, as the script verbs aren't really standardized.
There is a scripts section in pyproject.toml, which is leveraged by “poetry run”. This is different than for npm, though, since these aren’t dev-environment scripts but the executable scripts that are installed with the project
I'm pretty happy using Poetry, and agree with your initial point, partially with the second. There can be some edges with packages involving "anything" binary (to be fair, that is to be expected), and a big issue (for me) is locking the resolution of some libraries, like boto (since botocloud has hundreds of patch releases and the resolver can get pretty crazy unless you play a bit of manual bisection). But this only hits you on poetry lock or poetry add when developing, and only in some cases, I think it's a fair price to pay for a reproducible build.
I don't recall it having custom commands but in my opinion this isn't the job of a package manager.
If you really want a "just works" experience when dealing with C extensions, you should freeze your development environment one layer up (e.g. VMs, vagrant images, what have you) so that you can always successfully install and compile your C extensions because the underlying system is also kept under version control. And this is independent of whether or not you are working on a Poetry or an NPM based project.
It's not that hard. I suspect that you're just used to simpler conditions.
2 - Pretty much yeah