Is it efficient and sufficient though? And can and do we build real security on top of it?
This issue shows systems have been built for decades with blatant holes because it was not taken into account in even core os admin tools.
There is the other problem corresponding to the myth that everything is a fd. Which has never been true, and is even less and less as time passes.
Also, extensive extra security hooks and software using them are built, but not of top of this model.
Finally, sharing posix fd across security boundaries often causes problems because of all the features available for both sides, for which the security impact are not studied.
A model just stating that posix fd are capa is widely insufficient. So if this is the only one, even in the context in pure Posix we already know this is an extremely poor one.
That's it.