The studios are pushing hard on this. In order to get actors on the performance capture bandwagon, they have to convince the Academy to give an Oscar to a person for a virtual performance.
You see this in every frickin' video of Avatar where Cameron or the actors talk about the production. It's almost akin to a Bush-era media blitz how they parrot the same sentences again and again.. "This is not an animation --it was me!"
We cannot give an Oscar for best performance to a virtual actor.
This is a slippery slope. One of the entire reasons to use performance capture is to leverage the fact that it's all data. In a split second you can take the smile from take 6 and blend it into the nice squinting eyes from take 8.
Even the mere 'mapping' of a performance onto a character of different proportions alters it.
We shall see if their millions in marketing pay off, but I hope that there is no best actor or supporting nominee that didn't actually show up in a single frame of a film.
And I have worked on performance capture films.