They were refrenced in Rebels via a Holocron and I beleive theres a guide or something that came out that included them but don't quote me on that.
Edit: apparently this guide is where they are refrenced
Edit 2: The form shown in Rebels is Form 5s other variant Shien which focuses on blaster deflection
This book is actually different.
Where as Ultimate Star Wars and most visual dictionaries have spreads on specific characters or things and go into detail on them, this book has spreads on general topics and has a bunch of prop photos of them. It's even got spreads on things as trivial as food, luggage, furniture, and interior design.
Its amazon page has some preview pages to give you some idea.
EDIT: as far as interesting info goes I think the only treat we'll be getting is the re-canonizing of some of the trivial details found in the original visual dictionaries. But if I find anything juicy I'll be sure to post.
They do release these. The Visual Encyclopedia is basically exactly what you are looking for, although probably not as in-depth as what you have envisioned.
I'm holding out on picking anything up until after Episode IX releases though.