Some suggestions I would like to see:
Planetary interiors
Atlas mode (features alternate textures for Solar System planets, such as topographical and false color maps for terrestrial planets and moons, Continental Drift and thematic maps for Earth, historical and false color maps for giant planets based on either Pioneer, Voyager, Hubble, Cassini, New Horizons, Juno imagery, etc., mostly reused from Celestia Origin)
The Sun under various light spectra, with those textures represented as transparent overlays (for visible light, the Sun texture from Solar System Scope is used to represent the Sun's chromosphere), also flares and prominences on the Sun's surface
Venus' surface texture is now reoriented (its map texture is made upside down so that it is rendered right-side up)
Corrected models for certain asteroids and comets (again mostly reused from Celestia Origin) and new textures for certain dwarf planets like Haumea, Makemake, Eris, Sedna, Gonggong, etc. based on either Snowfall or Kexitt's textures (also from Celestia Origin).
Redesigned and more visible ring textures for Jupiter, Uranus, and Neptune (again also from Celestia Origin)
A redesigned Milky Way texture featuring a spiral bar
Asteroid and Kuiper Belts and Oort Clouds (seen only from far away)
Interactive educational features