I suspect the new API-level technology will be outlined at WWDC this year. Probably for a final release sometime next year.
My thoughts would be that Apple will use 10.7 to leverage a lot of the APIs that have been added in 10.6. Complete, pervasive, use of Grand Central Dispatch (even more than now).
Expansion of QuickTime X to provide modern OO APIs for editing that currently still rely on old-school C APIs and QT7. More codecs built into Quicktime X with an official plugin scheme for adding then (currently added codecs use QT7)
Possibly some generic API that opens up hardware acceleration for plugins in WebKit.