No time frame yet, the roadmap would be the place to watch. As a note, we are looking into possible improvements to OpenVDB in the Corona core (e.g. better overlapping of VDB objects, which currently is an issue) so we may not see any work done on moving this across until the core has had any updates (rather than work on porting something that is already undergoing improvements, may be best to wait til the improvements are done and working).