We don't know that they aren't swappable. And no one can entirely predict the future but a LOT of devices rely on USB-A, but also, 110VAC has been around for all of our lifetimes, and if something replaces USB-A we can very likely get a pocket-sized adapter. A few years ago I bought an external AC battery to power my laptop; it's about the size of a 25oz can of beer and weighs about the same, cost in the high 2 figures, and I'm extremely happy to not have to carry it anymore. Or to even feel like it's an absolute must that I get fully powered up before I board. It's been about 30 years since I started traveling with a laptop computer (they were way larger in those days and IIRC I inherited it from a senior member of my consulting team who had the juice to get one for himself but when he quit of course he couldn't take it with him), and it took them almost all this time to provide reliable onboard power. I'm pretty happy where things are at now power-wise. Of course I travel with a notebook and phone, but I don't own a tablet.