Tried just now with Safari, iOS 9.3.5, Vector skin, "desktop site", 9.x-inch Retina display, iPad 3, touch only (no Bluetooth kbd).
Just a quick test: deleted one word, tapped around the toolbar and publish-changes-related screens.
UI still fairly responsive. Feels just a teeny bit slow, but no worse than many sites on this older device. Only exception is the symbols list (omega button) takes a very long time to show.
I see now that you can already flip between Review your changes and Preview screens (dialogs, modes, views, overlays, whatever is the correct term). The relationship between these two screens and Save your changes makes more sense now.
I can see how people might want to publish directly from the diff or preview screens, but still think there is value in having them return to Save your changes before publishing. At the cost of a single click, it means they get a second chance to see the legal copyright note, and to consider their edit summary.
Perhaps the initial "Publish changes ..." button with ellipses could be renamed to "Review and publish..." to reflect its full function and distinguish it more from the second "Publish changes" button. I do notice on the smaller screen there is less free space on the toolbar to accommodate a second button.
Multi-line selection with syntax highlighting turned on works fine with Vector skin.
Bug? Can't paste into Edit Summary box on this platform.