It can't be Yonah. Yonah is a 32-bit chip and apple's OS has been 64-bit for a while.
AMD's Turion would work very well, and runs has a 25watt power envelope - perfect for the Mac Mini and available now.
By going with Turion, Apple could start shipping notebooks like these next month: http://www.msi.com.tw/program/products/notebook/nb/pro_nb_selling.php?UID=608 . Just re-compile their current 64-bit BSD based OS and apps for the Turion 64-bit chip used in this ultra-light that comes in Apple White or Business Black.