"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Another Mac OS X 10.4.9 (8P2120)
Apple seeded the 8P2117 build during Macworld Expo just last week, and has now released 8P2120 to developers today.
The new seed has a 40+ laundry list of fixes and under "Known Issues" it lists "None".
The last update (10.4.8) to Mac OS X 10.4 (Tiger) was released on September 29th, 2006.