Hey Aram
I tried to explain further up, but not having this feature does directly affect how big my phoenix grid needs to be which in turn affects the simulation time drastically.
As you can see in the video I linked to, the last step is reducing the final grid to just the area of focus, then enabling 'ocean' mesh to fill the rest outside of the sim grid, and then clipping the ocean mesh to your desired shape. But we can't do that because slicer won't let us. As you've said yourself, you'd need to shell and then clip, but how do you create an infinite shell to clip an infinite ocean?
So instead, we have to use 'Cap Mesh' instead of 'Ocean Mesh'. Cap mesh unfortunately doesn't have the same effect as ocean mesh in terms of filling outside of the sim grid. So I have to make the sim grid slightly bigger than the pool in my instance then clip using the shell method. But this means my sim grid is now wayyyyyy bigger than it would be if I could use ocean mesh.
See attached, you can see my two sim grids in green. If slicer allowed us to clip in the same way as vray clipper, then I could reduce that larger sim grid covering the entire pool to roughly the size of the one i've drawn in blue, as i'm only interested in the splash/foam at the base of the waterfall and not the entire 12m long pool