Sorry, but we can. Almost all the media in the world is in this format, your examples being special cases or practically irrelevant. In particular, your example of a DVD audio is special case, as it is actually in AC3 codec and it is desirable to pass it through the system as-is, because Dolby wants money for encoder implementations. The 96/192/5.1/7.1 are not really even relevant to the point I was making.
I was talking about performance. Nobody expects a mobile phone to spit out a 7.1 stream, ac3 or not, or whatever. I believe my point was that I wanted to argue for the case of simplified internal pipeline of gstreamer, where special case formats could be removed and replaced with more general ones. Your 7.1 192 kHz streams could be just 8 32-bit floating point channels for the purposes of the discussion, but I predict that you'd have severe difficulties transmitting those channels to amplifier.
See? This is not a point that is really worth discussing.