Bump! This has come up again recently as part of the work to move OpenUSD to the VFX Reference Platform CY2023. We’ve decided to remove support for building HDF5 from build_usd.py but will keep support in usdAbc so that anyone who wants to still use HDF5 can do so.
I posted an announcement about this here: Removing support for HDF5 from build_usd.py