4.7-inch iPhone 6 and the 5.5-inch iPhone 6 Plus
iTunes 8.1 "Coming Soon": Speed Boosts, TV/Movie Genius Feature and More
Apple's "What's New" page for iTunes highlights a few of the changes coming in the update, including speed boosts for library loading, iTunes Store browsing, and device syncing, expansion of the Genius feature to include movies and TV shows, and a change in the default audio import settings to 256-kbps AAC.
In addition to the highlighted features, Apple's "iTunes A to Z" features page suggests several additional changes, including updated Parental Controls that appear to add the ability to disable access to the entire iTunes Store while still allowing access to iTunes U content. The page also adds an entry for Autofill, which does not clearly specify what the changes are, although it appears possible that the feature implemented for the smallest-capacity iPods is being extended to all models.
Update: Based on new screenshots scattered throughout the iTunes pages, the iTunes "Party Shuffle" feature has apparently been renamed "iTunes DJ".