ECS
Zenyx should be backed by an ECS. ECS is a data-driven architecture for games which allows massive optimisations of cache and parallelisation as each system operating on data has to declare its dependencies beforehand.
Currently, we are planning to use sparse sets for the backing datastructure of components. So the first task would be to implement efficient sparse sets for the core engine. A nice feature while doing this would be per backing array allocators as this helps to reduce copying when adding and resizing components.
Zenyx's renderer abstraction should make it possible to write simple rendering code for game objects. It should be graphics API agnostic as that would ease adding other graphics-APIs later. Such as Vulkan by the Khronos group for raytracing since wgpu does not support it.