You're the man when it comes to this:
The Android Keyboard.apk that is on the replicant images.. how come it's twice as big as that on F-Droid?
Inspecting all this with baobab shows that the
res/raw folder takes up most of the size of the zip. This is where the dictionaries are stored. The actual difference is that the Replicant version has support for more languages (22 vs 9 from the F-Droid apk), so there are more files in there!