As the lines between FF and crop continue to blur - and we are seeing very high performance crop bodies ....
Assuming you're referring to Canon crop cameras I think your premise is false - unless by "performance" you're excluding what ultimately counts, image quality. Over the past few generations of Canon crop bodies there has been negligible improvement in sensor performance - the images taken with a 70D don't look much different from images taken with a 7D, 60D, or the last few years' worth of Rebels or EOSM, even if it's now easier to reach that result thanks to better AF etc. The gap in price between crop and FF may be narrowing as the price of the 6D continues to fall, but if anything the gap in image quality between crop and FF has been widening: cf 5DII vs 7D/60D/Rebel and 6D vs 70D/EOSM - the crops have stayed much the same, but the 6D is noticeably better in image quality than the 5DII, which in turn is still considerably better than any of the crops. (And even when/if Canon does start to introduce crop sensors with significantly improved image quality - 7D2? - the various physical traits referred to by the short-hand phrases "crop factor" and "full frame advantage" will remain.)
Is this really true that FF IQ is so significantly superior to crop ? I think the market is moving rapidly to smaller bodies and smaller high quality lenses. Sure there are certain aspects of FF especially in the area of DOF that are not achievable with a crop, but ultimately the prosumer like myself, will not justify the cost of FF bodies and lenses. I still think there is a new much bigger prosumer market - that will go for high quality lenses for crops.