Let's be clear: there are two stories here. The first is the release of OpenGL 4.5 and the second is the announcement of the "Next Generation OpenGL Initiative". They both occur on the same press release, but they are two, different statements.
OpenGL 4.5 Released
OpenGL 4.5 expands the core specification with a few extensions. Compatible hardware, with OpenGL 4.5 drivers, will be guaranteed to support these. This includes features like direct_state_access, which allows accessing objects in a context without binding to it, and support of OpenGL ES3.1 features that are traditionally missing from OpenGL 4, which allows easier porting of OpenGL ES3.1 applications to OpenGL.
It also adds a few new extensions as an option:
ARB_pipeline_statistics_query lets a developer ask the GPU what it has been doing. This could be useful for "profiling" an application (list completed work to identify optimization points).
ARB_sparse_buffer allows developers to perform calculations on pieces of generic buffers, without loading it all into memory. This is similar to ARB_sparse_textures… except that those are for textures. Buffers are useful for things like vertex data (and so forth).
ARB_transform_feedback_overflow_query is apparently designed to let developers choose whether or not to draw objects based on whether the buffer is overflowed. I might be wrong, but it seems like this would be useful for deciding whether or not to draw objects generated by geometry shaders.
KHR_blend_equation_advanced allows new blending equations between objects. If you use Photoshop, this would be "multiply", "screen", "darken", "lighten", "difference", and so forth. On NVIDIA's side, this will be directly supported on Maxwell and Tegra K1 (and later). Fermi and Kepler will support the functionality, but the driver will perform the calculations with shaders. AMD has yet to comment, as far as I can tell.
Image from NVIDIA GTC Presentation
If you are a developer, NVIDIA has launched 340.65 (340.23.01 for Linux) beta drivers for developers. If you are not looking to create OpenGL 4.5 applications, do not get this driver. You really should not have any use for it, at all.
Next Generation OpenGL Initiative Announced
The Khronos Group has also announced "a call for participation" to outline a new specification for graphics and compute. They want it to allow developers explicit control over CPU and GPU tasks, be multithreaded, have minimal overhead, have a common shader language, and "rigorous conformance testing". This sounds a lot like the design goals of Mantle (and what we know of DirectX 12).
And really, from what I hear and understand, that is what OpenGL needs at this point. Graphics cards look nothing like they did a decade ago (or over two decades ago). They each have very similar interfaces and data structures, even if their fundamental architectures vary greatly. If we can draw a line in the sand, legacy APIs can be supported but not optimized heavily by the drivers. After a short time, available performance for legacy applications would be so high that it wouldn't matter, as long as they continue to run.
Add to it, next-generation drivers should be significantly easier to develop, considering the reduced error checking (and other responsibilities). As I said on Intel's DirectX 12 story, it is still unclear whether it will lead to enough performance increase to make most optimizations, such as those which increase workload or developer effort in exchange for queuing fewer GPU commands, unnecessary. We will need to wait for game developers to use it for a bit before we know.