They created a specification for the PKGBUILD format and a library to parse PKGBUILD files.
If you wanted to use PKGBUILD files to build Ubuntu or Debian packages, you could in principle build your own makepkg implementation for building Ubuntu packages.
You could also build an SBOM tool that takes a PKGBUILD and produces the SBOM using the PKGBUILD metadata of all the transitive dependencies.
They are also working on something that could be summarised as "IDE" features. Validation and linting of PKGBUILD files not unlike what a language server/IDE does (e.g. rust analyzer or IntelliJ).
EDIT:
There is also a library for programmatic creation of PKGBUILD files, so build systems could integrate with it to automatically produce Arch Linux packages. This could make building your own Arch Linux packages even easier than it already is.
Aren’t PKGBUILDs just shell scripts?
It's an implementation detail, you're saying it like they're completely free form. Not really, they have a very specific structure that every package adheres to.
Parsing them currently requires evaluating them as shell scripts. Should be obvious how bad of an idea it is, especially in the context of the AUR (which is why it requires you to push a dumbed down metadata file called SRCINFO along with PKGBUILD — which is then used to show package info in the web UI you're probably familiar with).
Being able to safely parse PKGBUILDs without running them would certainly be an improvement.
Well, I have seen PKGBUILDs with arbitrary logic defining the metadata:
https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=webor...
Which is what necessitated a separate, statically-parseable .SRCINFO.