No, I'm afraid that I won't be covering the Struts integration stuff. As you know, the 2nd edition was quite long and that's because it attempted (and failed) to cover *EVERYTHING* about Spring. As I approached the 3rd edition, I knew that the goal of covering everything was even more impossible. So I set out to focus on the topics that I thought would be of interest to the majority of the readers. Struts didn't make the cut.
Besides...Struts 1 support was originally supposed to be removed from Spring 3. It somehow stayed in there after the final release...but it's eventually going to go away. As for Struts 2 integration, that might make a nice topic for a blog post, but my guess is that it probably doesn't appeal to the majority of readers. So, it will not be in SiA3.