R20: Rockman & Rockman X Official Complete Works (released in the west by UDON as separate volumes) is easily one of the best and most definitive art books for the Mega Man series. And in honor of Mega Man's 25th anniversary, it's going to get republished with additional content as "R20: Revised Edition" (currently a tentative name).
To bolster the book's contents, manga artists Hitoshi Ariga and Yoshihiro Iwamoto will be submitting special illustrations just for the book. Other additions are being planned, but will come to light at a later date. I'd wager that Mega Man 9 and 10's contents would likely be added, since they came out after the original "R20" was published.
Additionally, a major Q&A for all Mega Man series artists is being prepped (which even includes Xover), and they want fans to contribute their questions. If you use Twitter, you can submit your questions with the hashtag "#R20増補" for consideration. You can submit as many as you like, but certainly not all of them can be addressed (and I doubt all your "why is Capcom killing Mega Man?" questions will be). The deadline for questions is October 11th at 1PM, Japan time.
With as awesome as the original R20 was, I can only hope they'll add plenty more!
News Credit: Rockman Unity