Looks so much better with that SwiftKey keyboard. I don't mind the height itself in the Apple keyboard and it might be alright to type with, but it just looks displeasing to me personally.
Well, this is just what it looks like in the app itself. When you are actually using Swiftkey in other apps it looks like this:

As you can also see, it doesn't adapt its colour to the apps settings like the Apple keyboard does. But still as a Dutchman I can't live without SwiftKey as the Apple keyboard still doesn't give you word suggestions. But more importantly I type a lot in English too and with SwiftKey you don't have to switch between languages as it understands when you are typing in Dutch or English. It's fully multilingual, no need to tap that globe every time you want to type a word in a different language like on the iOS keyboard.
Is there any possibility to add the grey space bar when using SwiftKey?
I don't think they have updated their app for iPhone X yet, but I can only assume they will make some colour changes to it.