Can you show me where you're getting this information from, as I can't see any reference to it.
The only thing I can find is that you have to "Enable Full Access" to allow text prediction, but this is allowing the keyboard extension to access the index of previously typed words stored within iOS, there's no reference I can see to sending keystrokes to the developer.
Does it say somewhere that it sends keystrokes, or are people just misunderstanding what Enable Full Access is about?
I got over the fear finally and became a happy user of SwiftKey already. I read their privacy policy and they claim that they will not send over your typing information to their server unless with specific permission from user to open the "cloud" stuff. I think it's the wording of apple that confused us since the iOS warning clearly states that by allowing full access we are giving the app the permission to send the data over the Internet.