As I understand, this thread only discusses syntax and ordering rules for version numbers.
 
But if users see the :semver in ASDF examples and documentation, they will likely assume full semver practice is recommended by ASDF. As semver does not work for Common Lisp, I am afraid such encouragement of its use will have lasting destructive effect on the ecosystem. So, if this new logic of version numbers is to be implemented, I would suggest to name it somehow differently.
 
Also, if the motivation is the desire to distinguish alpha versions from stable releases and have alpha ordered before the stable, the following approach makes it possible in the current versioning:
 
alpha version: 3.4.0-alpha
beta version: 3.4.1-beta
stable version: 3.4.2

In other words, never publish versions that have equal numeric parts. IMHO there is no significant practical sense in keeping even the least significant (patch) number equal between alpha and release.
 
Best regards,
- Anton
Best regards,
- Anton