Here's some things I'd personally like to see in future Starfinder products (at least one of which I've mentioned on other threads):
Rules for creating vehicles other than starships or mechs.
Rules for applying weapon fusions to vehicular & starship weapons.
Rules for creating stationary facilities (space stations, outposts, shipyards, etc.).
More equipment & weapons (a la the Starfinder Armory), including new & variant bio-, cyber-, & magitech augmentations.
Rules for creating new alien races, perhaps as a companion to the Galaxy Exploration Manual set to debut next year (possibly involving a contest with the winning entry being featured in a future Starfinder product, be it as an Alien Archive entry or as part of a new Adventure Path).
More of the uncommon Pathfinder races (i.e. gillmen, merfolk, vanara, etc.) brought into the Starfinder setting (one possibility being having gillmen in an underwater-themed Adventure Path, introducing them as genetically-engineered creations of the Azlanti Star Empire).
A mythic-level Adventure Path centered on the mystery of the Gap (and possibly featuring Golarion's reappearance, with all the fallout that comes with it).
A mythic-level Adventure Path centered on the "Great Old Ones" (i.e. Cthulhu, Hastur, Yig, etc.), their Outer God masters, and their various servants.