The second CF card will never happen. The mechanical redesign issues would be too costly and in any case the 702 is already a consumer-cost reduced version for people unable or unwilling to put out the money for the higher capacity internal device versions. If you need more capacity, buy a 722 and put in a big SSD. Of course the 7xx devices will write to FLAC if you really need the extra space with what you currently have. If you want a live back-up, the 722 will record to internal drive and compact flash simultaneously. The newer versions of 722 firmware also write to firewire devices in parallel. So maybe just upgrading to the more feature rich current machine would meet half your list.
I'm not really sure what you mean by "act as a mass storage device'. I load my 722 with other files all the time instead of carry a second external storage device when I'm on the road. I've used it to park files from a camera when I needed to dump the video recorder each night and still used it to record sound the next day.
As for lower power, there is a tradeoff when selecting components and design. They could likely reduce power consumption but there will be a complementary compromise in the quality of the resulting system. It's not like they are power hogs anyway. I run an external preamp with it's own power supply so I get seven hours between battery changes on the 722. That seems pretty good.