While a Veskarium supplement is definitely high on my wishlist for future books.. I also would love to see Starfinder Player Companions. It seems like at the moment the Adventure Paths are filling this niche, but with Pathfinder I absolutely loved having those small, regular volumes focused on particular themes.
Other things I'd like to see are supplements on magic, technology, and the faiths of Starfinder with character options to help craft characters around these aspects. Plus, I'd love anything that might explore Solarians more as these would likely do.