The floating laser base, hydraulic build platform, and floating build resevoir (my favorite of the three) all give the Peachy a fixed focal point. If we're getting to the point of microstructures though, lensing turns out to be absolutely essential. I did a quick browse through Wikipedia about diffraction and found that (according to the papers linked on the first page) while reflective diffraction needs structures to be in the order of 10x the wavelength of the light you want to exhibit as the viewed color, aperture diffraction becomes a problem at the aperture being below about 6-7x the wavelength of light passing through it. The problem becomes not one of lase size, but of how much resin is partially cured by light scattering and refracting within the resin itself. In the macroscopic scale, this has no effect on a hard ridge, but microscopically, it would cause any corners you make to be deeply rounded off by partially cured resin.

Granted, having a microtexture of gently rounded divots might also have interesting optical effects, just not the deeply iridescent coloration of sharply etched silicon.