Preview at WWDC likely in June, followed by September launch.
Magic Keyboard, Magic Mouse 2 and Magic Trackpad 2 References Found in OS X 10.11.1 Beta
A new Apple Wireless Keyboard and Magic Mouse 2, each featuring Bluetooth 4.2 and rechargeable lithium-ion batteries, first appeared in FCC filings in August. Apple also registered several new web domains related to the term "Magic Keyboard" in September, including applemagickeyboard.com, applemagickeyboard.net, and applemagickeyboards.com.
Apple currently sells an Apple Wireless Keyboard, Magic Mouse and Magic Trackpad, each powered by two AA batteries, so these newly uncovered accessories are in all likelihood next-generation versions. The new Magic Keyboard, Magic Mouse 2 and Magic Trackpad 2 could have Force Touch, which is built into new MacBooks, while the inclusion of Touch ID is a more unlikely possibility.