This is great! It was fun and quick to make for instance a water pattern! 
One thing I wish was different is that when I changed from SeExpr to Simplex Noise, I lost my original water test on SeExpr, I would love for it to remember the changes so when I go back to SeExpr it is back to how I left it. Or a little warning telling me that I will lose my changes if I change mode, and ask me if I’m sure if I want to change.
Great work on this so far! Excited to see it developed further!