The feature I most need, which I'm not sure whether you're able to do, as I'm not sure if its an issue with Flicktype or Apple, would be the ability to continually review the text of a previously written document with flicktype. Ex. If I write a 10 paragraph document, whether using flicktype or not, dismiss flicktype so that the text then leaves the flicktype cursor and enters the document, then later enter flicktype to edit that text, I can't actually review that text beyond the first line with Flicktype. A half-screen feature *MIGHT* fix this.
I also use flicktype for fiction writing often, so my suggestions, in order of importance would be:
Half screen keyboard
iCloud sync: (I alternate between my iphone and ipad often on the same project and updating dictionary entries on both is cumbersome.
Customize symbols keyboard: The ability to add quotation marks to my most used punctuation marks would be an amazing time saver.
Beyond this would be extra polishing features which, while really nice, wouldn't be essential to every day use.
Tap sound on touchdown instead of lift up: ( just makes the app feel snappier)
Flick left and hold for quick delete
Flick sounds, new sound scheme, and customisation seem grouped to me.
iPhone 8+, iOS 11.4, public beta 1.