The lattice deform lpe goes in this direction, but you most likely want many waves: lattice deform does not have enough control atm, and if it had, moving all the handles by hand would be painfull. Moreover, you certainly are not interested in fine tuning the result, but only on the global aspect.

I think it can be worth writing a specific effect for that. There are many aspects you would like to control globally: magnitude and wave length, plus the same for a few harmonics, random strength/size, decay, choose between cartesian or radial waves... or the waves could be generated by superposing many circular waves around random points, like rain drops. There are many choices to make, and a blueprint is a good idea at this point.

The best would be to make it as general as possible (maybe someone will come with it's own preferred deformation right after that one is implemented?). Maybe, we could have a dialog where you enter the "deforming" formula ( dX(x,y)=..., dY(x,y)=... ) but I'm affraid this is too technical, and would terrify the user. Maybe worth another lpe ;-)...

Cheers, jfb.