Very low-pop worlds would actually be viable if Settlement control were entirely out of player hands. The main issue with low-pop worlds is no Company is likely to be able to afford lots of high-tier upgrades in a Settlement. If that were completely dev controlled and independent of population and players, it could work and even be interesting being forced to move around to different settlements occasionally for your crafts.
Queues for instanced things like Outpost Rush would need to be cross-server though, to rustle up enough players.
Imagine a low pop world but surrounded by your helpful friends that play around the same time every day you do. An actually helpful community.