Rome hasn’t been built in a day and it sure takes at least a few years to create a fully functional mobile GPU. This is why Apple has been working under extreme secrecy for a few years, according to Fudzilla's Deep Throats in the graphics industry.
The news that Apple is making its own GPU makes sense as the outfit has more money than it knows what to do with and it has some experience with inhouse chip design. Apple has surprised many when they announced its first in house developed ARM based CPU cores. Developing an in house GPU would just be a continuation of the tradition. Having its own GPU would help Apple to compete better in the phone and tablet market. Of course it is unlikely to drop any price, it will just mean its huge margins will get bigger – if it can get the GPU to work of course.
Samsung has been developing a mobile GPU for more than half of a decade and has nothing to show for it. Apple is making its GPU to cut the cord from Imagination Technologies a company that makes its IP (Intellectual Property) for the GPU. The fact that there is a chance that it might not go is probably the reason you have not seen it hyped to heaven in the Tame Apple Press yet.
The key element of success is that Apple can spare a large portion of its silicon to get better GPU performance. Usually Apple makes quite large SoC chips compared to the competition but a larger chip means that there is more space for the GPU.
The company won't launch a new SoC based on its own GPU until it has something worth showing and it might take even years to see it in market. However we would expect to see Apple SoC with a custom CPU and custom in house GPU sooner rather than later.
One more thing, we are quite sure that Apple is not developing its in house LTE / 4G modem, it has already given the work to Intel for the future iPhone .