I don't think it's overly ambitious to address a number of these points, as most will be common to ASWF projects and CI.
1) The VFX Reference Platform build environment and dependencies is a general goal for the ASWF CI and we'll have a working group on that this week. Please join us (although, I know the time is a little inconvenient for the UK)
2) Larry's proposal for robust dependency discovery modules for CMake projects would address this specific problem nicely. Although the Ubuntu provided boost version is old, it seems to be more a case of the ambiguity / variety of boost library decoration choices that has caused the build regression.
3) We should now have the requisite knowledge and support to incorporate the OpenVDB Houdini builds and tests into the ASWF CI. I think that we were waiting for the project adoption and repo transfer to be completed so we should be good to start moving on that. I'll follow up with an email.
That really just leaves us with the broken build as an open problem.
I defer to the OpenVDB project and others but my 2c: pybind11 is definitely a worthwhile step, but I expect that is a non-trivial effort and that it would create changes in the OpenVDB python bindings such that we couldn't really build a VFX Platform 2018 or 2019 artifact.