"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Intel Xserve July, Mac Pro (Intel PowerMac) in August?
Meanwhile, PowerMac revisions (Mac Pros) are expected to make the transition to the recently announced Core 2 Duo processors (codenamed Conroe). These processors are expected in July.
ThinkSecret speculates that the PowerMac revisions would come at WWDC, and indeed, MacRumors has received confirmation Intel PowerMac revisions ("Mac Pros") are to be announced at the WWDC Keynote which takes place Aug 7-11, 2006.