We've been experimenting with 3d nebulae rendering in Blender since 2013 at least. Here's a dump of our test renders and stuff.
All rendered in Blender, Cycles. 100% procedural, no fluid sims involved.
https://www.youtube.com/watch?v=qpC8bp1eRh0 - Watch the teaser of our upcoming Nebula course
The Nebulae video course CG teaser