My point is that I wouldn't be too confident that a PDW700 w/ 24p would sell for over $700 more than a PDW700 w/o 24p in 2015. (I even more doubt you'd ever see a $4,500 investment turn into profit just through re-sale.)
Maybe it is just the economy driving used prices down, but I'm seeing camera prices cliff dive after a couple years on the market. Please correct me if I'm wrong, but it seems like par for the course now is 4-5 years on the market, one newer generation released & down in re-sale value by 50-75%.
Right now there is a F350 on ebay for a buy-it-now price less than the cost of a new EX1R.
The F800/700 are at the pinnacle of ENG/EFP cameras and you are unlikely to see anything that will knock them off that perch anytime soon. What else can Sony or anyone else do better? The cameras are nearly perfect. Perhaps a hgher bit-rate might be nice, or more fps for slower slow-mo, but there's not much else you could do to improve an F800/700.
Camera companies make money by selling new cameras, so they'll probably find away to make something new that people will want to buy. You're right with the higher bit rate, h264 or flash media, all of those can be "fixed" by a Nano Flash or Ki Pro mini.
But higher fps, 3D & larger chips are the three things that the F800/700 could easily be threatened by.
Probably these cameras will get their rightful life span, but I think current owners need to keep an eye out for networks to hop fully onto the next bandwagon when the next new camera comes out, be it 3D, large chips (shallow DOF), or ... ?