The OpenGL ES 3.1 specification adds support for compute shaders, now supports separate shader objects, supports indirect draw commands, adds in enhanced texturing functionality, improves the GLSL shading language, and has new optional extensions.
These new features to OpenGL ES 3.1 are mostly derived from existing features of the desktop OpenGL 4.x specifications, such as the compute shaders support. AMD and NVIDIA will likely be shipping proprietary driver updates soon for their Linux binary blobs to support GLES 3.1. When it comes to the open-source Mesa/Gallium3D drivers, while Intel was quick to reach OpenGL ES 3.0 compatibility, it will likely take a while for OpenGL ES 3.1 support to be officially reached. The open-source drivers still have a lot of work done for reaching OpenGL 4.0/4.1/4.2/4.3/4.4 support and thus blocking some OpenGL ES 3.1 functionality.
More details on the OpenGL ES 3.1 specification release can be found at Khronos.org. The Khronos Group is expected to have some extra announcements this week during GDC concerning their other industry standard APIs.