This attempt at restructuring GDDR5 comes a bit late.
Should have been released before.
AMD already transitioned to HBM (which is far superior to GDDR5 in terms of saving the physical space reducing the GPU size, as well as lowering power consumption whilst offering huge increases in speed and bandwidth).
I might only see this being used in Nvidia's Pascal, but even that is questionable as Nvidia has intentions of releasing Pascal with HBM2 (once it becomes available to them).
On that note, AMD has priority access to HBM2 (much like with current HBM1) which is in limited supply, and will be used on their new GPU's with (finally) new architecture and lower manuf. process.
On that end, Nvidia will have to wait until Hynix releases sufficient amount of HBM2 to them, which probably means delays for Pascal.
Alternatively, in order to release 'something' next year in any appreciable time frame, Nvidia might either use GDDR5X for Maxwell rebrands, or will possibly use them for Pascal.
Since Nvidia has more monetary resources than AMD, I can see them using GDDR5X as a way to release Maxwell rebrand cards to have something on the market, and then finally Pascal (once HBM2 becomes available to them).