I like standards and abhor bloat, but I must admit there are GNU extensions that are so useful and well known that it would be difficult to do without. Probably this happens when POSIX specs are too strict or feature-poor to be of use even for medium-complexity tasks.<p>One example is "make": I'm afraid that a POSIX-only implementation wouldn't run most Makefiles out there!
I’d love to see what performance benchmarks look like. The old ones were highly optimized, but perhaps for different challenges than today’s architectures present.