@voldapet -- thanks for your pointers.
WRT community themes, there isn't much. The market for e-ink devices is very small. I am working on a grayscale theme, which already works quite well for my purposes.
Two things perhaps --
1. I use Locus in the field (bike touring) to generate routes if the need arises. A key element is the presence/absence of camp sites or such, so I've changed the theme to display camp/caravan POIs at the smallest scale possible. So far so good. However, when I've added picnic sites, which are far more numerous, rendering screeched to a halt.
My understanding is that Locus' engine renders all the tiles that are visible at a given zoom level. If the user figures that something is wrong with rendering and zooms in, in order to reduce the number of features to render, the engine will keep going on the previous task before computing the new set of tiles. Which is odd because unless I am wrong, changing the theme kills the current rendering operation and starts a new one.
2. A related question is what are the best practices for POIs icons. Looks like the source is an .svg that the engine scales to the right size, from which it creates a .png copy that is cached and used as needed. If the icons were always rendered at the same size, irrespective of the zoom-level, would it make sense to pre-render the icons (i.e. link to properly sized icons)?