"if RHEL 10 requires the x86-64-v3 baseline, ISVs will be able to rely on it, too. This reduces maintenance cost for some ISVs because they no longer need to maintain (and test) AVX and non-AVX code paths in their manually tuned software."
I'm not really convinced by this statement.
If an ISV is really investing the effort to manually tuning their software for AVX and non-AVX scenarios then this means to me that this specific software is something that is performance critical and profits siginficantly from having AVX. This makes it very likely that the vast majority of their customers also have an eye on performance and most probably have invested in new server hardware.
So it wouldn't be an issue for the ISV to say that they support RHEL10 and they additionally require a x86_64-v3 (or AVX) capable CPU for their software.
The only thing that requiring x86_64-v3 for RHEL 10 as baseline would make easier for this ISV is that the ISV doesn't have to put the text "requires a x86_64-v3 capable CPU" into their datasheet/manual. And maybe adding a small script to their installer that complains if x86_64-v3 is missing.
Kind regards,
Gerd