I think it's interesting more in the sense of understanding what Unix is today. It doesn't really read as an argument against a Plan9-like realization of everything-is-a-file.
I'd summarize those posts in two main points:
1) Linux isn't a research project.
2) Bringing a Plan 9-like realization of everything-is-a-file into modern Unix really just creates an even uglier chimera than Unix already is.
Still, it's possible that open/read/write/seek is just not the right abstraction in all cases. http://yarchive.net/comp/linux/everything_is_file.html is interesting reading.