The ability to run Stable and experimental version and their saves from steam independently... ie as with "Satisfactory" and the Epic games platform... pretty please...
You can already do this by simply copying your entire game folder out of Steam, then include the game from Steam's menu " Games : include a non-Steam game to my library". A window will pop up asking for the game's .exe location ; just navigate to your copied folder and point to the EmpyrionLauncher.exe, and that's it.