ARM is moving on to the Midgard architecture and the T6xx series of GPUs, like Mali T604 (2012) and Mali T658 (2013), for high-end smartphones and tablets. At the same time, they are not forgetting about the mid-end and low-end “volume” markets, for which they have prepared a new chip called Mali 450.
The Mali 450 design will have twice as many cores (8) as Mali 400, and be twice as powerful, most likely when compared to the Mali 400 GPU in the Galaxy S2. That should put the new Mali 450 in the same performance range with the overclocked 4-core Mali 400 found in the Galaxy S3, which is currently the most powerful smartphone GPU on the market.
The Mali 450 GPU is based on the same architecture as the Mali 400, and it's really just a Mali 400 with twice as many cores, at the same clock speed. This means that manufacturers can increase its clock speeds further, just like Samsung did with their Mali 400 in Galaxy S3, so the 450 should extend the life of the Mali 4xx series. The difference between the 450 and the Mali T6xx series, is that the Mali 450 will continue to be used in lower-end devices, giving them the performance of high-end devices from just a generation or two ago.
Mali 450 doesn't support OpenCL and GPU computing, like the Midgard architecture does. These new features will be introduced in the T604, but T658 should really smash all mobile records for GPU computing next year, thanks to cache sharing between CPU and GPU. The Midgard architecture should also support the upcoming OpenGL ES 3.0, while Mali 450 will be limited to the current OpenGL ES 2.0.
Without giving too many details, ARM has also quietly announced that there's a new GPU coming after Mali T658, in 2014, codenamed Skrymir. I can only assume that Skrymir will be at least twice as powerful as Mali T658, in both graphics and GPU computing performance, and should be manufactured at 20nm or even 14nm. Skrymir should have support for ARMv8 64-bit architecture, just like Mali T658 does, and it should be paired with the next-gen 64-bit CPU that will come after Cortex A15 (still unannounced).