Because a custom keyboard can draw only within the primary view of its UIInputViewController object, it cannot select text. Text selection is under the control of the app that is using the keyboard. If that app provides an editing menu interface (such as for Cut, Copy, and Paste), the keyboard has no access to it. A custom keyboard cannot offer inline autocorrection controls near the insertion point.
Custom keyboards, like all app extensions in iOS 8.0, have no access to the device microphone, so dictation input is not possible.
Finally, it is not possible to display key artwork above the top edge of a custom keyboard’s primary view, as the system keyboard does on iPhone when you tap and hold a key in the top row.