Current version of raylib is quite complete and functional but there is still a lot of things to add and improve. Here it is a wish list of features I would like to add and functions to improve.
Note that around the raylib source code there are multiple TODO points with pending revisions/bugs. Check GitHub Issues for further details!
raylib 1.x
[IN PROGRESS] LUA scripting support (wrapper to lua lib)
Basic GPU stats sytem (memory, draws, time...)
Procedural image generation functions (spot, gradient, noise...)
Procedural mesh generation functions (cube, cone, sphere...)
Touch-based camera controls for Android
Skybox and Fog support
raylib 1.5
[DONE] Support Oculus Rift CV1 and VR stereo rendering (simulator)
[DONE] Redesign Shaders/Textures system -> New Materials system
[DONE] Support lighting: Omni, Directional and Spot lights
[DONE] Redesign physics module (physac)
[DONE] Chiptunes audio modules support
raylib 1.4
[DONE] TTF fonts support (using stb_truetype)
[DONE] Raycast system for 3D picking (including collisions detection)
[DONE] Floyd-Steinberg dithering on 16bit image format conversion
[DONE] Basic image manipulation functions (crop, resize, draw...)
[DONE] Storage load/save data functionality
[DONE] Add Physics module (physac)
[DONE] Remove GLEW dependency -> Replaced by GLAD
[DONE] Redesign Raspberry PI inputs system
[DONE] Redesign gestures module to be multiplatform
[DONE] Module raymath as header-only and functions inline
[DONE] Add Easings module (easings.h)
Any feature missing? Do you have a request? Let me know!