Despite there being only a hand full of comments on the entire Proscenium board, it would appear that the Proscenium team doesn't have time to answer them.
In regards to this particular subject (that being hardware accelerated video textures) I don't think this is going to happen. I've personally spent the last year speaking to every person I could think of at Adobe, Away3D and even folks on the Proscenium team. The bottom line is that to do this Adobe must facilitate this capability. Away3D and other API providers cannot overcome the current obstacles to realize this feature. This all begins with Adobe providing access to these capabilities to the other API developers (Away3D).
When Proscenium first came on the scene, I immediately contacted the Proscenium team requesting this feature. I thought since Proscenium itself was being developed at Adobe, this features could be developed (at least as an experiment) more quickly. Alas no. I've gone so far as to contact several Adobe Evangelists telling them that the Away3D team would like access to this feature. Again, no. Just silence.
So, if want to create truly hardware accelerated video textures using a 3D API, forget it. (especially for mobile). Isn't going to happen. This is particularly true for iOS, where native H.264 support isn't supported on AIR.