This page talks about what it takes to port webkit to another platform: http://blog.cranksoftware.com/webkit-porting-tips-the-good-t...
The GP post mentiones Plan 9, which is a great example here. There are real people who use Plan 9 every day (I have met some of them!) but Webkit will never be portable to that OS because there is no C++ compiler. This doesn't make the OS non-functional, but it does mean step one to porting a modern browser is "port GCC or LLVM," which is a massive task by itself.
Both Firefox and Chrome source code repositories are in the hundreds of megabytes, even without the required host OS dependencies vendored in. The document you linked to recommends leveraging freetype, cairo, and all kinds of other things that would require serious graphics infrastructure of a sort that's just not feasible.
Modern web browsers are keystones that cap off arches built of hundreds of pieces of very specific software. As time goes by, they require more infrastructure, not less -- c.f. Firefox, where to build the latest version you must also have a Rust compiler that targets your operating system. As the checklist of requirements grows ever longer, the candidate operating systems capable of meeting those requirements grows ever shorter.
Five years from now, I predict the only three operating systems capable of interacting with the web in any meaningful sense will be linux, macos, and windows; bsd and haiku et al will have been left by the wayside.
Ten years from now I predict there will be four operating systems, and one of them will be Fuchsia, because only a megacorp like Google has the resources to accomplish that.
That is an interesting prediction. What do you think will cause the BSDs to be left by the wayside in such a short timeframe, when they are more than capable of running the latest browsers right now?
Is the browser becoming a systemd module?
I am a little concerned about the trend to push "hardware acceleration" into everything. Graphics cards and their drivers are the biggest source of grief in PCs for me.
This lets you take advantage of whatever benefits your desired system provides you without a change of user experience.
It may be easier to have everyone use the same software and hardware platform everywhere. After all we do want interoperability and we do want everyone to play well with others, but, standardization and portability is a push to stop people from trying new things. The push to standardize everything is an unfortunate consequence of not having a separation of concerns, separate concerns such as content and UI.