[Coco] CoCo 3 68000/RAM board project

[Bookworm]

I have a suggestion for a CoCo 3 hardware project. I am not an engineer, and
can't design it myself, but I think it sounds like something that might work,
and be very useful.

There have been at least two attempts, maybe 3, to put a 68000 in a CoCo. The
first plugged into the cartridge slot and used the 68008, it's own 512k RAM, and
an optional VGA like monochrome monitor as peripherals.

The second was the Burke & Burke Rocket. It would have replaced the 6809 with a
68008. IMHO it would have been a great idea if the 68008 was compatible with the
6809, but it wasn't and required an emulator ROM.

The third was the FHL QT CoCo, a hard drive system that could be upgraded to a
QT Plus computer, but would the CoCo have still been connected?

My idea would be to put a 68000 on a CoCo 3 RAM board, with part of the RAM
being shared by both. The GIME chip already has a 16 bit buss to the RAM for
graphics, so the RAM is already both 8 and 16 bits. The only hard part I can
think of would be making the two CPU's able to stop and give the other control.

Can a 68000 or 6809 be memory mapped in the others address space?

This would (theoreticaly) allow the CoCo to run OSk in a NitrOS-9 window, and
could be used to display some of the type of graphics used on the internet and
considered too complex for the CoCo 3 all by itself.

So far, I just want to know if it could be done.