Dolphin needs OpenGL ES3. In fact, OpenGL ES2 + lots of extensions would also be fine, but it's much easier to say which ES3 feature we don't use than which ES2 extension would also be needed...
ES3 is backward compatible with ES2 doesn't mean there only some little differences. ES3 pulls in almost all changes from desktop GL3.3 (but geometry shaders). Just look at all this small changes in GLSL130 - it's a almost a new language... On desktop GL, we've also dropped all glsl versions before 130 (eg checkout intel ironlake support) as there are too many small pitfalls. So even if you manage to run dolphin fine on gles2+every extensions, I bet my next ogl change will break it again as nobody but tegra4 will ever be able to test this :-(
ES3 is backward compatible with ES2 doesn't mean there only some little differences. ES3 pulls in almost all changes from desktop GL3.3 (but geometry shaders). Just look at all this small changes in GLSL130 - it's a almost a new language... On desktop GL, we've also dropped all glsl versions before 130 (eg checkout intel ironlake support) as there are too many small pitfalls. So even if you manage to run dolphin fine on gles2+every extensions, I bet my next ogl change will break it again as nobody but tegra4 will ever be able to test this :-(