I like the way that Commodore made CD32 FMV card.
It was additional chip that generate video signal and mix it with amiga video.
Nice, elegant way of good old style of doing things.
No transfer to video memory, independent upgrade of hardware for movies, and you still can have amiga graphics on top of MPEG.
It will be good to se something like that even for vampire, it will save time of vampire team and precious cells in fpga.