Ahhh thats awesome! I didn’t see that. Makes sense, iirc someone at Epic said they saw volumetrics as playing a big role in “next gen” effects.
Honestly if you have time I’d suggest you check it out regardless as it’s pretty straightforward and might be fast enough for what you need. Ryan Brucks has a blog post on the topic, it explains how it’s set up in the volumetrics plugin and it’s actually relatively easy to work with, all the heavy lifting is done by the EncodeVolumeCoordinates and VolumeTextureFunction functions, which are both already included.
My guess is that it would probably be part of Niagara, you can create/manipulate render targets inside of Niagara and I would guess it’s probably faster than exposing it to BP.
In fact if I had to guess, I’d say it’s what they’re using as part of their flip fluid sim in the Niagara Fluids plugin… may also be worth checking that out 
Edit3: Looks like it it is indeed being used for the Niagara Flip Fluids! Found a few Grid3D modules that write to volume render targets!
Unfortunately the actual module content is all way over my head, I have no idea how any of this works but you may be able to parse it. I’ll have to look through their Grid2D+RT in the sample content and see if I can apply it to 3D. Either way, it looks really promising!