Shameless plug: I'm actively working on a similar project, Datoviz [1], a C/C++ library with thin Python bindings (ctypes). It supports both 2D and 3D but is currently less mature and feature-complete than fastplotlib. It is also lower level (high-level capabilities will soon be provided by VisPy 2.0 which will be built on top of Datoviz, among other possible backends).
My focus is primarily on raw performance, visual quality, and scalability for large datasets—millions, tens of millions of points, or even more.