A communication application with experimental PQC support would be
another example, and indeed if liboqs is intended to ever mature to
something usable in a security-sensitive use case, it would make sense
for people wanting to add PQC support to use liboqs now and then
upgrade their PQC support to "not experimental" once the library was
declared ready for security-sensitive use.
Do you have actual examples of applications which need to use an
obsolete version of this (let's be honest, security sensitive) library
which is declared to be unstable? And the concern is that the library
will evolve to not build on stable debian, but the application will not?
This smells a lot more like rationalizing than addressing practical
concerns.
This library in particular? No, but I've run into this situation with
other software in the past, even in distros less stable than Debian.
I don't really see how the concerns you're expressing are practical,
they seem to be "I don't understand why anyone would use this". The
only practical concerns I can see are archive size (haven't heard any
concerns that the archive is getting to big so far) or maintainership
burden (there's someone interested in maintaining it for now and the
project doesn't look massive), and both of those concerns apply to
every package in the archive. There are people actively interested in
both packaging and using liboqs in this thread, if I'm understanding
correctly, so "why would anyone use this" doesn't make sense as an
argument to me.