for what i know the away3d is moving to flash 10 due to the fact that its run faster and have very cool add ons like the pixel bender that the engine can use, the issue with the matrix was due to the fact that in Flash 10 the matrix3d apperaed, so in the branch it was recalled, is youre going to use version 9 of flash no need to recall it, in fact the flash 9 it havent by killed cause theres still a lot of pc that uses it, not for performance, right now some stuff runs faster in fp9 but its going to be faster in every aspect in the full release of away3d for fp10, so its like making updates to windows vista (belch) having windows seven or os X for free...
i dont know its just my opinion im not developing in away3d, i just think it may be the reason, its wasting time that could be used for the fp10 branch.
