SVE2 is an extension on top of SVE which some stuff already implements. The issue is more likely to be the politics of moving to ARMv9 than anything else.

As to SVE though, I'd guess variable execution time makes the implementation require a bit of work. Normally, multi-cycle tasks have a fixed number. Your scheduler knows that MUL takes N cycles and plans accordingly.

SVE seems like it should require N-M cycles depending on what is passed. That must be determined and scheduled around. This would affect the OoO parts of the core all the way from ordering through to the end of the pipeline.

That's definitely bordering on new uarch territory and if that is the case, it would take 4-5 years from start to finish to implement. This would explain why all the ARMv8 guys never got around to it. ARMv9 makes it mandatory, but that was released in 2021 or so which means non-ARM implementors probably have a ways to go.