having high bandwidth on a chip is all well and good, but it does not replace the fact that the CPU itself and the RAM is still traditional silicone. It is like giving a Ford pinto full access to a 100 lane highway... kinda cool, but mostly useless.
There are still 2 things that will be really neat to come from this tech:
1) There is still active development for actual photonic CPUs (not just CPUs with photonic buses) which will be really cool in 40-50 years.
2) Much sooner than that, imagine this kind of tech being used as a buss system on a motherboard to replace something like PCI Express. This would allow nearly infinite bandwidth to things like GPU, RAM, and storage with far fewer pins, and lower power consumption (and presumably heat).
For more info see IEEE's report on the chip here: http://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/processor-with-photonic-interconnects-built
It reduces the power consumption significantly and is probably very good for signal integrity (hugely important for high capacity and/or high performance memory). This is in no way useless.
It's silicon, not silicone. One letter can make a huge difference
Darkbreeze is also correct in that your analogy is flawed. Regardless of that, it isn't just more bandwidth between parts of the CPU (which is much more useful than you realize), it's more bandwidth per square mm and that's hugely important. That alone saves power, reduces latency, improves yields, and reduces costs. Furthermore, simple improved bandwidth between parts of the CPU improves performance, especially multicore performance. I imagine signal integrity can also be improved as the light wouldn't have to deal with electrical resistance, potentially increasing maximum stable clock frequency.
I doubt fully photonic CPUs are even a realistic goal. Light-based memory is nowhere near as effective as electrical/electrically controlled memories, let alone any difficulties in making a practical CPU core that processes with light.
I can see your 2) suggestion being practical. Light-based data transmission has been shown time and time again to be superior in most ways to electrical data transmission and that's one of the next logical steps. I don't think storage pin count can be reduced much (SATA already only has four data pins), but PCIe data pin count certainly could be reduced.