WWE has added CM Punk to summer SmackDown live events starting from the June 23rd show in Springfield, IL through July 29th, when Randy Orton's suspension ends. Sheamus is also advertised for those events, so you will have the WWE Champion and World Heavyweight Champion appearing on the same show unless something changes before then.
As previously reported, John Cena has been booked for SmackDown television tapings for the summer as well.
Orton's 60 day suspension reportedly ends on July 29th, and WWE has him listed for SmackDown live events starting in early August, including the brand's tour of Japan. Due to the time-frame of his suspension, Orton will miss the 1000th RAW in his hometown of St. Louis on July 23rd.