One result of iOS 8's size classes is that lots more apps support landscape orientation, and I have a confession to make: It drives me bonkers. I almost never want to use my phone in landscape. It used to be that most apps only supported portrait orientation, so it was no problem if you tilted the phone a little too far. It might send a rotation message to the app you were using, but the app would just ignore it. That means I could read Twitter while lying on the couch without worrying that the screen would suddenly rotate if I tilted a couple of degrees too far. In iOS 8, I find myself more and more tempted to use the rotation lock feature.
In fact, I leave auto-rotation enabled for one simple reason: video. Most video fits far better in landscape orientation than in portrait. The iPhone's screen is perfectly shaped for wide-aspect video in landscape. Unfortunately for me, iOS won't rotate video into landscape orientation unless it can rotate the whole OS into landscape. Put another way, if I use rotation lock to keep the phone in portrait orientation, that applies to video as well. That means video gets letterboxed into a postage stamp-sized area in the center of my screen.
I see how the behavior makes intuitive sense; it's the easiest to understand and doesn't require any weird special cases. iOS simply presents all interface elements so that they're oriented right-side-up relative to the device.
But video is a special case. It's displayed full-screen, so you don't have to worry about other interface elements. (There are elements like player controls, but they hide automatically after a few seconds.) It's far more likely to be sized for a landscape-oriented screen. People often rotate their phone to watch a video, then rotate back to portrait. If you have rotation lock enabled, there are quite a few extra steps involved: Open Control Center, disable rotation lock, close control center, then repeat the process to re-enable rotation lock after the video ends.
One way to deal with this would be for iOS to automatically present full-screen, landscape video in landscape orientation, regardless of the device orientation. Opening a video with the device in portrait orientation, the video would at first appear to be "sideways." Just as they do now, most people would simply turn their device to see it in the proper orientation. I don't think it would be all that confusing.
Alternatively, iOS could ignore the rotation lock setting for full-screen video playback. Users could leave rotation-lock enabled, but video players would still auto-rotate with the device as though rotation lock were off. When the video ended, the phone would revert to it's rotation-locked orientation. Nothing would change about the way things work with rotation lock off. In other words, video would auto-rotate even with rotation lock enabled.
Of course there are a few edge cases and gotchas to both of these solutions, but they'd both be an improvement over the status quo. Especially given how wonky activating Control Center can be, there should be an easier way to deal with video playback orientation then turning rotation lock on and off all the time.