Thanks guys. It was a nice mental challenge, but there are things I can't get to work properly, like you can see here. Foam streaming down the rock. I gathered the height mask could be displaced by using the waves a a basis, so when the wave subsides, foam streams after it, but I couldn't get the height mask properly done without using final position, which cannot be displaced. It's not a great deal to me, but it would be nice if that would work.
Furthermore, the vertically animated foam off the rock doesn't really go vertical
And I guess a nice feature request would be to have the possibility for one object to sit on something (waves/plane), and can be 'populated' (or updated) with every frame, so you don't need a (not properly working) population of one instance to follow the waves.
The positive about not using a water shader (nor a compute terrain) is the speed. This animation took 2.5 hours (detail 0.4 AA3).
