As you know I implemented the support of symbols files in dpkg-shlibdeps/dpkg-gensymbols, and I would be very pleased if libc6 could start using it as most packages would then benefit from weaker dependencies on libc6 and be more easily installable on previous versions of the distribution (sid package directly installable on etch in some cases).
Some time ago I tried to get the ball rolling by providing a first patch in #462444. Unfortunately the glibc team has not been able to finish the work up to now and the base freeze is approaching… so it would be great if some people could jump in, make the required changes, test and propose a new (fully working) patch. I just sent a message to give some indications on how to get forward, hopefully that will help anyone who wants to tackle this.
Thank you for your help!