The sand looks like simple geometry at the moment, I imagine it could be (relatively) easily implemented as a second particle type as part of the same simulation. The granularity of sand makes it pretty similar to liquid, it would just need adjusted properties (weight, friction, appearance)
>The granularity of sand makes it pretty similar to liquid
Sand behaves much differently than liquid. The friction between sand grains is not like viscosity and it lacks surface tension too. I don't know any continuous model that describes the movement of sand similar to Navier-Stokes for liquid.
I lost touch with the CGI industry, but sidefx latest release of houdini includes a dry and wet sand (snow, ...) simulator.
https://www.sidefx.com/index.php?option=com_content&task=vie...
They used to be on the fore front of this kind of R&D, so I guess it's pretty state of the art (as a CGI package of course).
The only thing that seems to be missing is the movement of sand as water sloshes over it. But I guess it would be more difficult to simulate tiny solid particles suspended in turbulent water. For now, let's just say that this beach is made of cardboard :p