I am quite happy with the pdf.js default viewer, which does not have react dependencies and does not need to download a meg or two to work. It does not require me to allow all kinds of scripts from the website or even third party scripts from random CDNs. It also does not need a purchase of a license. It has so far always been snappy for me.
So unless the feature set of this is so unimaginably great, that it completely revolutionizes PDF viewing, I doubt, that I will ever have a use for it. Maybe a PDF reading focused website could offer it as an alternative viewer, while obviously still preserving the option to view in the standard PDF viewer. Maybe that would make sense then for people, who need it fancier.
I would rather render PDF with a native app either as provided by the computer or device or the built in one in Chrome or similar.
The reason for that is that we tried pdf.js earlier this year and it is very CPU/mem hungry once you go past simple PDF's it becomes noticable.
Also rendering 5-6 single page PDF's in the same web page made Safari bog down.
This is what PDF.js is...
> PDF.js is built into version 19+ of Firefox.