GL|ES 3.0 is not in any way a modern API, like all of Khronos' crap. They gave up on a modern API when they abandoned Longs Peak. Their APIs are still based on the ancient C-based crap of OpenGL 1.0, just with more features bolted on in sometimes very awkward ways.
Originally Posted by wargames
The feature set of GL||ES 3 is still lacking compared to GL 4.3. There are some important additions over GL|ES 2.0, but there's a reason there's still separate standards.
Patent-free texture compression is worthless if the hardware doesn't support it. The compression is not as good as contemporary compressed formats, so it's a bad choice for minimizing download time, and it can't be loaded directly into hardware and used, so it's a poor choice for efficiently using VRAM. However, implementation needs to happen soon, as delaying implementation just pushes the date we can use it further back. Driver/hardware has to support it today so the market begins getting saturated with capable devices 4-5 years from now.
In any case, real OpenGL with all the patented crap is important. Without it, Mesa is mostly just good for running ancient Quake 3 derivatives and simple compositors, not modern AAA games or high-end visualizations. GL 3.3 makes GL tolerable to use (still needs waaay better devs tools, better error reporting, a real test suite for less buggy drivers from the big vendors, and so on outside of what Khronos considers its responsibility). GL 4.3 adds some critical features that D3D has had for over 3 years, though it still has some catching up to do. GL|ES is a compromise for limited hardware, not the future of professional graphics on PCs.