This is planned as soon as Packwiz releases its installer.

(For now, vanilla is supported by the MultiMC download, read here for instructions)

Edit: alternative script is being worked on in this repo: https://github.com/Fabulously-Optimized/vanilla-installer
If that one gets ready first, it will be (initially) recommended.

I can code a Python script that does this.

I can code a Python script that does this.

Appreciate the offer, but I would prefer contributions to the original thing (so, Java).

Okay. I'm not that good at Java so I'm not planning to work on their repo (at the moment)...

New potential alternative: https://github.com/Gaming32/Superpack

It has a working jar, but it seems a bit early to do any public testing with it.

An update, https://github.com/Fabulously-Optimized/vanilla-installer isn't ready, but it does work. So that's progress...

Update again...I would say the core functionality is finished, we just have a few more things to do (if you know Python and would like to contribute, we'd appreciate it :P)

I don't really have much of a release (even alpha or beta) estimate in mind yet, right now it's get the open issues closed and get packaging stuff done (which is arguably quite hard, taking Linux into account haha).

Done! Announcement:
https://floss.social/@fabulouslyoptimized/113340036497357027