I too look forward to it, no hurry :)
At the moment I use the EMI RTP API to act on immediate price changes, but am very keen to get the PRS to predict a few more things.
My Tesla power walls were installed on Thursday and I've just asked my retailer to put me on ToU plan so i've got my powerwalls charging from solar and grid during off-peak and using the powerwalls to consume power during peak periods. I'm in the middle of going a step further to check wunderground.com for the forecasted cloud cover so I can decide whether I just charge from solar during off peak day, or whether I need to charge from the grid too.
The end goal is to eventually look at the PRS data and have the powerwalls charge before an event occors, for instance if it works out cheaper to charge during peak time than the non peak, then do so.
Look forward to the next API releases :)