Hello there. I am not that experienced in FX, but it appears like the mantaflow realtime bake is being worked on: Sebbas Development Report
I can’t really comment on the OpenVDB stuff though, only that I’ve seen quite some other users requesting support. If it interests you, there was a gsoc project which was aimed at doing that (https://wiki.blender.org/wiki/User:Gskchua/GSoC2018/Final_Report, but it doesn’t seem that active anymore. Brecht (the lead developer of cycles) wrote a proposal a bit more recently (New object types), so I guess you should ask him directly (maybe tag him here).
And, as a side note, because you mentioned the particle system, there is currently work ongoing by Jacques Lucke to replace it by a completely new node based system (there is also UI discussion going on atm, consider adding feedback as long as it’s still in dev phase: Particle Nodes UI).