I noticed that on the Apple HIG, it says that custom keyboards should not implement emoji or dictation buttons because they are shown below custom and default keyboards. This is amazing news since native dictation was always a sorely missed feature with custom keyboards!
https://developer.apple.com/ios/human-interface-guidelines/overview/iphone-x/
https://developer.apple.com/ios/human-interface-guidelines/overview/iphone-x/