This page has a list of tasks that have a high level of priority.
A quick overview of the rendering technology used in SuperTuxKart. The game uses a highly modified version of the Irrlicht engine. The current render (codenamed antarctica) uses Lightprepass for solid materials and currently alpha blend materials aren't affected by the light.
If you want more in depth details about the engine you can read here a more technical overview
Improving the shaders management system
Currently the shader system isn't modular and require a lot of changes just to add for instance a texture. The task is to modify the current system and create a better system that allows to quickly load/unload a shader
For more information about this task, read the ticket on github
Refactoring the scene manager
One of the last thing remaining of Irrlicht is the scene manager. The current system uses lists to store objects and it causes all sort of performance issue. The task would be to refactor the scene manager and use a tree structure to increase the performance of the engine, especially in complex scenes.