Soft Particles
Particles look pretty harsh when intersecting other meshes and terrain due to the intersection of the particle plane. A technique called soft particles can be employed to soften the effect, leading to seamless transition between particle intersections. Such scenarios are quite common in both base game and modded areas, lava vents to braziers to mist effect would all benefit greatly from this.
This should be a completely optional graphical improvement as soft particles can have a significant performance impact. The implementation should be pretty straightforward, no significant architectural changes are needed.
The technique itself is quite old but still remains pertinent, especially with how we currently handle particles.