It seems to me that if Debian provides a Chicken 2.3 package for
stability reasons, then Debian should also provide a 2.3 eggs package
and keep it up to date. Using chicken-setup is inherently "unstable"
from the perspective of Debian stable, since the eggs are constantly
updated and haven't gone through the Debian release cycle. If you
care enough to run Debian stable, you don't want to do this. If you
want to use chicken-setup, you should use the latest stable version of
Chicken, which to me implies compiling or using Debian unstable (if
available).
I know that seems Draconian, but getting eggs to work on earlier
versions of Chicken is not always easy. Dependencies may change,
features may not be available, etc. I think it would be a massive
pain to maintain such a thing, not to mention the infrastructure isn't
there, although Felix can be surprising.