It's a successor to WebGL, along the lines of newer graphics APIs like Metal/Vulkan/DirectX 12. Google and Mozilla are also developing a C-compatible library that should be available as an OpenGL alternative for native code.
So if successful it might end up as the most convenient cross-platform graphics library (across desktop/mobile/the web). Currently the alternatives in this space are:
- OpenGL (which Apple has deprecated and is stuck on an older version on their platforms)
- Vulkan, which is the lowest level and most difficult to get started on of the APIs, and also doesn't work on the web, but is supported on Apple systems by using the MoltenVK library to translate it to Metal
- some non-standardized libraries written by third party developers like bgfx and Oryol.
For the shading language they settled on a text based language designed to be easily translatable to/from Vulkan SPIR-V bytecode, with the goal of being able to re-use existing shader compilation toolchains (and most of the work put in to SPIR-V), while still having the ability to write/read shaders without a shader compiler. Also SPIR-V files are fairly large and apparently don't compress well with standard algorithms (see SMOL-V) so the text based format should probably be more efficient to transmit on the web.