In addition to being able to minimize the vertical margins (please!
), I'd also be interested in the ability to slow down Siri in the text-to-speech. In Settings -> General -> Accessibility, there is a slider for controlling how rapidly Siri speaks. I don't know if this control is usable by third-party developers, but if it is....
Oh, and as long as I'm on the subject of accessility...VoiceOver support could be improved by having no unnamed buttons.