We're revealing a secret book at raywenderlich.com next Monday - post here to guess what it is and have a chance to win a free copy!
I think it would be “Algorithms in Swift”.
I’m going with a Unity book.
“Beginning Windows Phone Development” is logical next step for RW 
book about Siri framework…
A recipe book containing all the Margarita recipes tested at RWCon?
I think “Algorithm and data structure using swift”
This was easy! The title of the book is “How Cobol programmer turns into Swift coder in 24 days”
CloudKit by Tutorials.
Something like a collection of recipes for making users comment your published articles maybe?! you guys definitely know how this works… 
And it is… Server-side Swift Programming - Your swifty mobile backend
Although I know the chances are low, I would love such a book after the release of Swift 3.0, because every good mobile app has a better mobile backend. I’ve recently done some research about this and I think Swift has really the potential to be a good server-side language.
I’m going to hope that it’s either Sam’s diary or a Swift Algorithms book. Hoping for the former, but either will do 
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Something around BOT development (AI stuff) using siwft.
I think the book on either “Architecture and Design Patterns in Swift” or “Algorithms and Data Structures in Swift”.
Something related to Unity development.
I think it is going to be “Programming with SubJective-C” a brand new language compatible with Swift, Objective-C and Java.
I’m hoping for a macOS book, I’m sure whatever it is will be useful.
It will be macOS by Tutorials?
something about web framework swift based
How to make MacOS app while eating tacOS