Provide a set of starter project templates - FPS, third person, sandbox, blank - so creators can hit the ground running with a working foundation instead of starting from scratch every time.
Would be super nice if S&box had a powerful Sandbox gamemode, as in Garry's Mod, to serve as a base game for others. The Sandbox right now is kinda barebones.
This is fundamentally so important for the game and platform's success. A box of tools developers can use to make game modes, maps, etc. It provides a baseline standard, and allows for inexperienced folks to learn quickly and try things out.