Ubuntu 24.04 LTS exists and needs only RV64GC and will be supported and enhanced for many more years.
Debian has no plans to require more than RV64GC.
RVA23 is a very good thing in certain markets, but nothing forces you to support it for a personal project.
I cant see debian remaining on rv64gc later on when enough rva23 boards are purchasable
Why? It'll still run fine.
Just like Debian still runs on original x86-64-v1 from 1999, not x86-64-v3 (needs AVX2,FMA, BMI1, BMI2, LZCNT) or even x86-64-v3 (needs AVX-512).
Similarly, Debian for arm64 still requires only ARMv8.0-A from 2011 not even ARMv8.2-A (everything from A75/A55 to A78/N1/V1) let alone ARMv9-A (A710, A510, X2 and on).
Why would they do in the RISC-V world what they totally haven't done in amd64 or arm64?
No, debian requires ARMv8.0-A + FP + NEON, as those are optinal extensions (even optional in ARMv9.0-A)