In the absence of information about how this is actually going to work, I'm concerned it really hasn't been thought through. I experienced tablet IFE on a recent AA flight (albeit in First class) and it was not a stunning success:
- they were stored in a cart, and were distributed and collected at the end of the flight by the FAs. They wouldn't have been able to fit more than about 16 of them in the cart due to their bulky carry-case.
- they were powered with a plug-in adaptor; this clearly requires power to the seat but overcomes the battery issue
- they came with a small stand so that you didn't have to hold them for the ~2 hours of your movie, which is good because otherwise you'd have a mighty sore hand and the tablet would quickly get a build-up of grubby skin oil on it. Conversely you needed to have your table down to put them on, I'd be concerned that in economy you'd get such a sore neck from essentially looking down at your lap
- mine had a software glitch, the first replacement I got was missing it's power cable and the second was the last spare one on-board
- the FAs really had the irits with the whole process; it caused them so much more work than an IFE that they simply turned on.