I came rather late to this, but according to the history at http://wiki.debian.org/Multiarch
multiarch specification work started in 2004, but nothing much actually happenned on code until the spec was finalised in 2nd half of 2010 (which is about when I got interested). Initial glibc patches must have been written around then, but as Adam says, only got into the distro around end 2011.
You (David) are quite right that we didn't handle this upstream very well at all, and that has made the whole thing more painful than it needed to be. I saw everyone involved doing their best be inclusive, trying to avoid the exact problems we have in fact ended up with, but clearly we didn't get upstream glibc (and gcc) people involved soon enough and that's been a pain for everyone. I know I didn't even know who those people were until quite recently (It seems to me that both arm and Debian/Ubuntu - the circles I move in - have been quite poorly connected to glibc dev for some time).
I'd echo Carlos's sentiment: Lets put previous cock-ups behind us and try to get this sorted. I find multiarch to be a really useful and significant development and I'd really like to get to a state where it's easily available to people/distros that want to use it, and not causing undue pain for people like David. I'll try and help with that, but I only looked into glibc a few months back, and then almost entirely at packaging, so my contribution is necessarily limited.