@chaoslord
OK, so I was mistaken about the Minimig, but I'm 100% correct about the Natami and other FPGA based solutions. Adding new screenmodes and other capabilities is a matter of updating the softcore, no hardware mods necessary.
That is because the D/A on the Natami is already 24bit capable. There is nothing to stop you from adding the registers to the original minimig in principle, the problems start when you attempt to use/display them. If those "other FPGA based solutions" share the same or similar limitations to their D/A, they will suffer the same issues as the original minimig.
That is all.