Just to be clear, your statement "the move to eglibc isn't as much about creating a fork of Glibc" implies that Debian's use of eglibc creates a fork of glibc.
EGLIBC has been around since November 2006 or so. It is a fork of glibc, given this definition, "a project fork happens when developers take a copy of source code from one software package and start independent development on it, creating a distinct piece of software" -- http://en.wikipedia.org/wiki/Fork_(software_development).