SPIR-V appears to be the future of shader programming in the Vulkan/OpenGL space. However, GLSL is not going away anytime soon. GLSL compilers still ship with OpenGL and there's currently no sign that they will be removed or deprecated. The OpenGL specification still considers GLSL to be the primary shading language. 

However, if you're interested in getting on board with SPIR-V early, or you have an interest in moving toward Vulkan, it might be valuable to you to start working with SPIR-V now in OpenGL. Fortunately, that's possible, at least in recent versions of OpenGL.

The future of SPIR-V is very bright. There is already a (mostly complete) compiler for HLSL that targets SPIR-V, and it is likely that other languages will be developed soon. It's an exciting time for shader programming!