OK, I'm on 67% (Journalist - not sure whether to be sad or happy!) so there are realms above 64%, plus I'm not on "Hard" for any game as yet, just a few mediums. Noticed this morning that if you go into Progress Review and bring up your Expression Potential and tap Next, it will tell you how many words you have succeeded with and how many more you must use correctly to get the next unlock. Whether your potential will rise in the interim, I can't say, and the unlock may just be another game level - will have to keep checking.