You said that Apple shouldn't use Quicktime to support those features.
I didn't say that either.
Use what DVDs already have. ??
For DVD-Video format playback via Apple TV, yes, from existing DVD media and TS_VIDEO folders. Basically, DVD Player streamed to and controlled by

TV.
So I disagree - why not use the great compression technologies they already have in Quicktime. I don't want to download an 8GB MPEG2 based DVD, a 1-1.5GB MPEG4-10 Quicktime version is probably ample.
I'm not disagreeing about the possibility of DVD extras with iTunes Store purchases, just questioning how those extras might be distributed and doubting whether Interactive QuickTime or Matroska would be viable technologies for Apple to use. Certain "standalone" extras could be distributed separately but obviously that's wasteful for alternate audio tracks if you have to redundantly download and store entire video tracks with them.
Maybe that gives some context to what I actually said:
I seriously doubt Apple TV would ever have support for something that "resembles a DVD" instead of just supporting DVD-Video format/media playback directly.
That was mostly addressing "DVD media" compatibility, with an unintended implication to the "iTunes Store". Sorry for any confusion.
Restating Evangelion's original question a bit differently, how might DVD-like interactivity be achieved with

TV-compatible content? I thought more specific speculation about that could be interesting, with the possibility of learning from that feedback.