It is not about “seems can’t”, but more like “will not” as JDK 8 is the king and soon JDK 17 will be the new king (Next Scala 3 LTS version will increase minimum required JDK version), though it doesn’t mean that we will get full support for “-release:X” flag ([JVM] Use StableValue as compilation target for lazy val - #2 by sjrd).
I’d guess that it is much simpler (cheaper and realistic) to maintain single bytecode generator instead of having many feature-forks per JDK versions.