Bug fixes.
I appreciate any improvements you do for the engine, but I really feel like 3D is a pretty niche thing and there are a lot of basic things to cover still that will benefit basically everyone. For example, a workflow of using multiple objects types, it still has tons of inconveniences
Often you can't even change objects visibility settings when you select multiple object types, its really annoying. If you want to have "Button" family, you are forced to create a family for all of the needed object types and duplicate the logic, and so on. The engine will benefit so much from having something similar to JS arrays where you can store any object type and then work with their shared properties. Or "Is" operator that will allow you to un-abstract object from family to a specific object type. Instead you have to use Pick By UID for basically everything. It was already annoying 11 years ago when I started using the engine, and its still basically the only way to do most things