Here you can see a Video with a few approaches: https://vimeo.com/161247246 [vimeo.com]
And Here a Texture Cutting and Upres Technique https://vimeo.com/161699027 [vimeo.com]
You can find more Demos on my Vimeo.
I spent a long time figuring out the right Interface and Workflow during lots of test and used a Mari Style Bake Aproach. You paint a buffer that then gets baked. Similar to the Grooming tools but with the ability turn it off and on and do manual bake which becomes handy for painting lowres volume and then doing upres seen in the video above.
The Geometry gets loaded within a Python SOP that should be generated automatically. I only have tested on Linux so far so I hope it works on other Systems.
Thanks to the houdini stroke SOP you can plugin any input for the stroke projection in input 1 and paint on that.
At the end its still just a demo but for simple things it works.
I released a Non Commercial Version for download including a locked asset for testing.
Also included is an example showing the simple setup with the VDB SOPs + volume as mask. I am still looking for ways to manipulate the Volumes in VOP/Volume Wrangle. I found some nice way to get textures in there but its slow and I could really need some help on that side.
More Info: http://microbot.ch/new/vdb-painter/ [microbot.ch]
Documentation/Download: https://sites.google.com/site/vdbpainter/ [sites.google.com]
(Please Note my native language is not English so Documentation might be hard to read.)
All Feedback is very Welcome.