Those side keyboards might actually make the iPhone Plus almost usable for me, lol. Almost. Luckily the iPhone Pro/Edition/8/whatever will only be slightly wider, but even so this side keyboard might get some use.
The thing I'm most excited about overall is the redesigned iPad interface. It looks so much faster to move around now. I feel like the iPad is finally starting to come into it's own, distinct from the iPhone. Being able to work with files like this will make it much more feasible to work on larger design projects and possibly even websites. Does anyone know if multitasking apps can watch files generated by another app for changes and process them? I'd love to see a version of CodeKit for iPad that I could run alongside Coda 2 that could watch my web project folder and compile my SCSS changes for publishing (we've got a weird server setup at work and they won't allow me to run a compiler server side for whatever reason that I can't remember). It would be acceptable to do split screen for this to happen, but I hope in the future Apple will allow background utilities to run at set intervals on the iPad. Even if it's just one or two utilities at a time, it would make it a lot more useful.
As for the iPhone, I'm most excited about the new Control Center and the customization. I'm rather surprised you can't reorganize sections as it appears to be modular. I'm also looking forward to the new AirPod settings, as I'd love to set my left ear to pause and right ear to skip. I hope in the future they add a triple tap option.