Thanks, Pavel, for your comments.  You are in a big crowd regarding those who anticipate what Elon Musk will reveal about his battery comments.  Bottom line:  we don't know until it happens.  As for Lithium Iron Phosphate batteries you are correct in that they have been around for quite a few years, and for good reasons.  Their lower energy density is indeed compensated for by longer cycle life and by a better safty parameter.  I have had two electric bicycles for over a decade powered by Lithium Iron Phosphate batteries so I am quite familiar with them. Both E-bikes are still powered by their original lithium iron phosphate batteries and performing quite well to this day and have never been replaced.

I am a licensed amateur radio operator and lithium iron phosphate batteries are popular with many amateur operators for their positive features in powering amateur radio stations in a portable and remote site basis.

  Having said all of that I think it might be wise to wait and see what the "reveal" reveals.  Maybe something, maybe nothing but we don't really know until it happens.  I believe there are many new developents in batteries going beyond the original lithium iron phosphate design.  Musk has publically committed to taking as much Cobalt out of the batteries used in his Power Wall products and in the batteries used in Tesla for some time... that is not a new wrinkle on his part.  His reasons have both to do with safety and with economics.  Whatever Musk has up his sleeve I would be willing to bet that it doesn't abandon the use of lithium in whatever batteries we see from his corporation.