I have considered this for a 640x200 display, but it needs data at 400
nsec, on 4 bits. This is a little too fast for a PIC alone (a clock pulse
is also needed).

Smaller displays can be driven slower than this. You'll need a large PIC
with enough outputs to drive most address lines of the frame memory.
Almost the only option to allow the RAM to be accessed by another CPU is
cycle stealing from the other processor, which means that you can only
apply this with a processor that supports lengthened reads or such. I do
not consider the possibility that you might want to accept flicker ;)

my 2 bits

Peter

PS: A few PEELs seem to be a better choice for this imho ?

PS2: What would you use for a 32x64 driverless passive DSTN LCD for very
few offs and XY four-voltage drive ? I have a couple of 82C55 SMTs laying
around, and it will be an 8-bit system. Good ?