Is the following item also on the list: pHDF5 in combination with non-trivial data transform function and compression?
Currently, this combination is not possible because compression needs to be collectively while the data transform function should be done independently. This has been discussed in https://forum.hdfgroup.org/t/phdf5-1-12-data-transform-in-combination-with-compression-filter/8799. I have not clue how much effort it would take to make this possible, but maybe the mentioned item “Smarter about library-allocated memory (esp. filters & API calls that return library-allocated buffers)” could be a stepping stone for it.
Furthermore, the semantic versioning feature would be great feature for HDF5.