Emulator

Currently Dolphin will boot in landscape mode on Android and there is no way to achieve other orientations without the use of third-party orientation control tools. While I understand there are legitimate reasons for removing the automatic rotation behavior, it would be nice to be able to set the desired orientation before starting emulation. I personally use reverse-landscape as I use my volume keys for the L and R triggers.

As for UI, this could probably be added as an option in the base Graphics Settings menu. It might be interesting to have on desktop, but I personally don't see a reason for it.