I'm one of those users - I fly 150k miles a year, international and domestic - and in my opinion, we're better served by an external battery like this one:
Microsoft Surface External Battery & Car Adapter Charger
For $130 ($145 if you want a car charger with it) you get a battery that adds 4-8 hours extra life for the SP2 and has usb inputs to charge other stuff like your phone, etc. And you can use the (far better) Type/Touch 2 covers instead.
I haven't seen a price on the battery cover yet, but it's a fair bet it's going to cost more than the $130 the Type 2 costs now. Now, you could argue that with the battery cover you could just buy that and not a regular one, and use the USB port on the SP2 to charge phones, all of which is true, but you'll still be stuck with a sub-par (compared to the Type 2) keyboard that's not backlit, heavier, and you would need to have all the time whether you needed the extra battery or not. With the external battery, just stick it in your bag for long flights and you're set.
Again, I do agree that for a small - small - subset of users the battery cover would be more convenient - namely, those that need that extra battery every single day but for frequent travellers I think the external battery is the better, and more flexible, option.
Getting to be a moot point on planes anyway - even in Economy class I haven't had a seat without at least a couple outlets in over a year, but YMMV.