One of the core requirements for a keyboard extension is having a 'globe' button to allow users to switch to other keyboards. However, the iphone X provides a globe keyboard button by default - making this requirement redundant.
My question is whether a keyboard will be rejected by the App Store for not including a globe button on iPhone X only?
No, you should not include a 'next keyboard' button for iPhone X. When needsInputModeSwitchKey returns false you should not show this button.
>question is whether a keyboard will be rejected by the App Store for not including a globe button on iPhone X only?
Why would following the docs cause a rejection? If anything, I'd think it would be just the opposite, where including that icon on iPhone X would risk a rejection.
Reference - From the HIGs:
https://developer.apple.com/ios/human-interface-guidelines/extensions/custom-keyboards/
"Don't duplicate system-provided keyboard features. On iPhone X, the Emoji/Globe key and Dictation key automatically appear beneath the keyboard—even when using custom keyboards. Your app can't affect these keys, so avoid causing confusion by repeating them in your keyboard."
