take a look at all the mpeg 4 (vc-1 avchd ) movies and the video bitrate
Batman Begins VC-1 13.70
The Dark Knight VC-1 24.00
Iron Man AVC 27.13
There are titles like Indiana jones and the crystal skull that go into the high 30s. But your going to have an uphill battle trying to prove that it looks better or suffers less artifacts than Iron man or the batman movies.
There are more important things than bitrate and after a certian point you get demishing returns. Bluray was designed for mpeg 2. It was only after hd-dvd supported the new codecs did sony add them into bluray and bluray is better off for it. You can throw 200mbps at vc-1 and avc hd but its going to just go to waste and create storage problems.
Back in the day it was said the LOTRs was down at a 12mbps bit rate and looked spectacular on hd dvd.
Worry about improved lenses and sensors before you start to worry about bit rate.
And no... they can't raise the bitrate for avchd. It's a standard already... they'll at least have to call it something else if they do
avc hd profile 2 , avc hd part 2 , they can all it whatever they like. Just like SD cards went from SD to SDHC