Michael, let me ask two predictable questions. 1. When do you expect to complete the 3rd edition? Seeing as the book is being heavily reworked and knowing your attention to detail, I guess the answer is "when it's ready". 2. Will the Rails version be fixed at 4.1?
I expect to use Rails 4.1 unless 4.2 is out of beta in time to use for the screencasts. I've compartmentalized the version-specific material, though, so I'm cautiously optimistic that I can swap in new Rails versions (even in the screencasts) as they're released.