There's a big belief that OpenGL 5 will be about optimizing this cross-platform, widely-used graphics API. All of the major hardware companies are working towards reducing OpenGL driver overhead and making other OpenGL improvements as a result of AMD's Mantle API. Mantle is still Windows-only and used by just a handful of games for now with AMD's Catlayst driver on GCN GPUs, but it's ignited a conversation about increasing the performance potential out of OpenGL. DirectX 12.0 is also going to be optimizing the performance potential of Microsoft's 3D graphics API.
For those curious about some of the low-level OpenGL extensions that will likely end up within the 5.0 specification plus other OpenGL 5.0 features, the G-Truc website by Christophe Riccio has up a PDF that outlines candidate features for OpenGL 5. This document is worth looking over for anyone interested in OpenGL; it's a 34 page read.