You don't need a COCO3 any more 8)
Xroar plus some patches to emulate the Cloud9 IDE controller running FUZIX as a 16K Cartridge that loads the rest of itself off IDE disk on boot. Needs a 64K COCO2/Dragon64 (and testing on real hardware). A bit over 2K free with a 256x192 bitmapped display, so I now need to squash in some minimal partition table support. Once I fixed the discard recovery there should be another couple of K free.
It's just about possible to do a cartridgeless port but you lose the space for partition table handling, graphical screens (so you get the nasty upper case shouty text mode) and wouldn't have enough space to run some of the bigger apps.