PNG can and is often used in a lossy way. Reducing the number of colors so PNG8 can be used instead of PNG24/PNG32 is the most common way to do that. Tools like pngquant exist, and for example Photoshop when exporting to PNG also has an option to reduce the colors, to flatten the image (remove alpha), or to change the colorspace.
16-bit PNG files can easily accidentally be reduced to 8-bit, which is of course a lossy operation. Animated PNG files can easily get converted into a still image (keeping only the first frame). CMYK images will have to be converted to RGB when saving them as PNG, which is also a lossy operation. It can happen that an image gets created as or converted to JPEG and then gets saved as PNG - which of course is a bad and lossy workflow, but it does happen.
So I don't agree that with PNG there is no way to accidentally make it lossy.
In any case: lossless or lossy is not a property of a format, but of a workflow. For keeping track of provenance information and workflow history, I would recommend looking into JPEG Trust / C2PA, which is a way to embed as metadata what happened to an image since it was captured/generated. Relying on the choice of image format for this is fragile and doesn't allow expressing the nuances, since reality is more complicated than just a binary "lossless or lossy".
It's technically correct. Googlers (at Google Research Zurich) have been working on jxl-rs, a Rust implementation of JPEG XL. Google Research has been involved in JPEG XL from the beginning, both in the design of the codec and in the implementation of libjxl and now jxl-rs.
But until now, the position of other Googlers (in the Chrome team) was that they didn't want to have JPEG XL support in Chrome. And that changed now. Which is a big deal.
For lossless, bitdepth of course does matter. Lossless image compression is storing a 2D array of integer numbers exactly, and with higher bitdepth, the range of those numbers grows (and the amount of hard-to-compress least significant bits grows).
The OP article is talking about lossy compression.
When comparing lossy compression, note that lossy compression settings are not a "percent" of anything, it's just an arbitrary scale that depends on the encoder implementation. So lossy "80%" is certainly not the same thing between JPEG and JXL, or between Photoshop and ImageMagick, etc. It's not a percentage of anything — it's just an arbitrary scale that gets mapped to encoder parameters (e.g. quantization tables) in some arbitrary way.
The best way to compare lossy compression performance is to encode an image at the quality that is acceptable for your use case (according to your eyes), and then you just look for various codecs/encoders what the lowest filesize is you can get while still getting an acceptable quality.
Yes, my hope is that jxl can become an interoperable format for layered images. It does not have all the functionality of image editor formats (PSD, XCF, etc), but it does have a very useful subset of that (named layers with basic blend modes). For interchange, it would be very suitable since it has state of the art compression (both lossy and lossless), does not force you to merge the layers before exporting, while the images can be viewed directly by any application that supports jxl — since the blending happens inside the decoder, the viewing application can be blissfully unaware that it even is a layered image, it will just get the merged image from the decoder if it doesn't ask for the individual layers.
Though maybe some people think the JPEG committee is now creating spreadsheet formats...