Just for fun, I was fiddling with the arcbd and was able to get the MLDEMO to do something by adding this to a2arcadebd.cpp.
I don't know how correct this is, but they seem to run.
void a2bus_arcboard_device::write_c0nx(address_space &space, uint8_t offset, uint8_t data)
m_tms->vram_write(space, 0, data);
m_tms->register_write(space, 0, data);
./mame64 apple2e -sl4 arcbd -flop1 Amparcade_1983_Third_Millenium_Engineering_Corporation.do -debug
It's interesting that in this article from Creative Computing that the mountain scene gets horizontally flipped left/right.
and the VDPTEST program runs now
with the change: