It's also interesting to look at other architectures at the time to get an idea of how fiendish a problem this is. At this time, Commodore, Nintendo, and some others, had dedicated silicon for video rendering. This frees the CPU from having to generate a video signal directly, using a fraction of those cycles to talk to the video subsystem instead. The major drawback with a video chip of some kind is of course cost (custom fabrication, part count), which clearly the Macintosh team was trying to keep as low as possible.