I’ll revive the topic internally as @auzaiffe is not working on this anymore.
And there’s already another forum post about that I believe 
is this what you are talking about by any chance ?
I don’t how exactly this was made exactly but it could just be a custom cloud texture that’s updated in real time via a shader or else, no need to fetch cloud density at a point for this.
edit: this was apparently used a base for fluid sim