Support KMZ directly as map format, not just as map item.
Locus can already render ground overlay KMZs reasonably well as "map item" on top of existing maps. That works with "foreign" KMZs (eg from Global Mapper) as well as for Locus own creations (form the builtin calibration tool). Problem with this approach is that performance suffers quite a lot with these things, even scrolling gets very slow and jumpy with reasonably sized overlays. I suppose this is because Locus fumbles around with every single included image coordinate during every scroll? That can be quite a lot for a properly set up ground overlay pyramid... at least 50-100 for a typical use case (standard sized topo map sheet in 8000x8000 resolution, pyramided as 1024x1024).
My suggestion is to also support KMZ files directly as a map format, not just as "map item overlay". All the code is already inside Locus somewhere... only the actual loading needs to be tweaked a little... like distribute the ground overlay image pyramid into something that resembles your internal sqlite map structure.
As a result, we
a) could use locus-made maps from the integrated calibration engine directly without major performance loss.
b) have a reasonable interchange format to the professional GIS world that also works for huge maps. Most pro tools (eg GlobalMapper) export KMZ nicely and hassle free.
Obviously, an even more suitable pro format would be ECW of GeoTIFF, but thats another story :-).