This awesome experiment by Sebastien Menozzi supports terrain collision and real-time terrain edits. As the developer mentioned, his main focus has been on optimizations, allowing him to handle a significant number of particles on an M1 Max.
Currently, he is working on tuning slope collision stability and edge behavior. He hasn't shared detailed information yet, but will likely provide updates in the original Reddit post.
In the meantime, you might also want to play with this jello‑like MPM fluid by matsuoka_601 in your browser: