I'm going to miss it too
Not for actual typing, as I can type blind. But just for those times when watching a movie, reading something etc with no hands on the keyboard, and then the need arises to press a key. E.g. changing the screen brightness, changing volume, subtitle delay, etc. It's really hard to see where the keys are if you just quickly need to tap a single key. I always end up straining to see which is the right one. Especially with the function keys because I don't know them by heart. The fact that the symbols are grey on black doesn't help, they're very low contrast.
I loved the backlit keyboard on my MBP for this reason, I always had them set to the lowest setting and it was great like that. Not intrusive at all but seriously helpful in the evenings.
I do think Apple will bring it back, I'm sure it won't cost a lot and the thickness implications will be minimal if they use some kind of Electroluminescent foil. I hope they just had to redesign it and left it until the next update.