An APK analysis of version 9.6 of Gboard has revealed some major aesthetic changes and some good news on dark theme programming. Changes, as dug up by 9to5Google and seen here, may or may not be carried over to the public release.
A new "Default Dark" theme is set to join the "Default Light" theme that was seen in version 9.3. It seems that the app will utilize these colorways with a new "System Auto" dark theme toggle that will adhere Gboard to the current system status. We had hoped to see this feature with Android 10, but better to be polished than to experiment sometimes.
Design-wise, it also appears that the Roboto typeface may be switched out for Google Sans while the keys themselves have been packed in a bit tighter with the hitboxes (or borders if you've got them turned on) getting squeezed down. You may need to practice your fingering if these tweaks come through.