IMHO, android's libc is probably the best next option to glibc. The other choices leave alot to be desired, and are fairly disused these days.
Indulging internal developers is quite an interesting point.. Who ever created some of this stuff is really good. There are not many people in the world who could sit down and write a new ELF dynamic loader, libc and related toolchain goop - let alone start out that way and not be afraid of failing. This is arcane stuff.
I'd be quite interested to know how long it took to make, IMHO, a super expert, done this before, kind of thing, could probably knock it out in a month. You'd probably burn more time than that just fussing with glibc to make it smaller.