Hello,
I've mentioned my crazy project of interfacing a FPGA (board) with a NuBus Mac in another thread.
I'm opening a new dedicated thread as there is a significant update now:

This show the naked PCB on the left, the populated version without the required daughterboard in the middle, and the ready-to-use (if you can live without a proper bracket, need to 3D-print one) on the right.
As of earlier today, the board will pass POST in my Quadra 650, and the embedded declaration ROM (in the FPGA bitstream) will enable a single-resolution, 8-bits depth only framebuffer of the desired resolution up to 1920x1080, which is what I'm testing it with. This framebuffer will work as a secondary screen, the 'startup' screen (by moving the smiling mac in the Monitor control panel) or as the only screen by unplugging the monitor from the onboard video of the Q650.
The framebuffer in the FPGA should be able to support 1/2/4/8 bits and even full color, it was tested using my other (and more mature) project, SBusFPGA., but that is'nt supported yet.
Now for the disclaimers, warnings, and other caveats:

Special mention to the awesome folks who made the Quadra 800 version of Qemu, without that simulation tool to implement the DeclRom this might not have happen. Also to the entire Litex community, another FOSS/H project without which this would not have been possible.
The entire project is on GitHub (and is a bit of a mess, requiring files from various other projects including SBusFPGA and XiBus).
I've mentioned my crazy project of interfacing a FPGA (board) with a NuBus Mac in another thread.
I'm opening a new dedicated thread as there is a significant update now:

This show the naked PCB on the left, the populated version without the required daughterboard in the middle, and the ready-to-use (if you can live without a proper bracket, need to 3D-print one) on the right.
As of earlier today, the board will pass POST in my Quadra 650, and the embedded declaration ROM (in the FPGA bitstream) will enable a single-resolution, 8-bits depth only framebuffer of the desired resolution up to 1920x1080, which is what I'm testing it with. This framebuffer will work as a secondary screen, the 'startup' screen (by moving the smiling mac in the Monitor control panel) or as the only screen by unplugging the monitor from the onboard video of the Q650.
The framebuffer in the FPGA should be able to support 1/2/4/8 bits and even full color, it was tested using my other (and more mature) project, SBusFPGA., but that is'nt supported yet.
Now for the disclaimers, warnings, and other caveats:
- As mentioned previously, this is an expensive toy and nothing more - there's currently no plan to manufacture and/or sell them (if some established vendor wants to give a more cost-effective version a try, I'm open to supporting the project, but I don't have the time to do it myself)
- They are not easy to make; the PCB is only 4 layers but plenty of surface-mount chips including the large Xilinx CPLD (mine were professionally assembled by SeeedStudio, which also made the PCB)
- They are not easy to set up; the FPGA is simple enough, but the CPLD requires configuration via a dedicated JTAG programmer (which adds to the cost), and Xilinx tools have not been upgraded for years so I needed to hand over a USB controller via VFIO-PCI to a Windows 7 virtual machine just to program the d*mn thing...
- They are wider than a 'proper' NuBus card, so would block a neighboring NuBus slot; however in the Q650 (or the IIci) they fit in the innermost slot ($C for the Q650) with no issue leaving both other slots free
- Most of the gateware & software is super-early and not tested beyond being able to start SimCity 2000 and it looking OK
- Changing resolution dynamically would require changing the video clock dynamically in the FPGA, which is doable but difficult, so it's not on the TODO list (if you change monitor, changing the FPGA bitstream is easier and more efficient design-wise)
- Changing depth should be a matter of ROM/software support
- It's not fast. Quite usable in 8 bits, but noticeably slower than the Q650 internal video (even accounting for the larger area requiring more memory). Experience with the SBusFPGA shows that even on a faster bus, unaccelerated 32-bits truecolor is too slow to be usable.
- Acceleration should be possible, but is going to require a *lot* of software work and hardware-software codesign
- VGA output may have color range limitation (of unknown hw origin), so it's likely HDMI is the way to go
- Dual-head with HDMI and VGA is theoretically possible, but not really planned

Special mention to the awesome folks who made the Quadra 800 version of Qemu, without that simulation tool to implement the DeclRom this might not have happen. Also to the entire Litex community, another FOSS/H project without which this would not have been possible.
The entire project is on GitHub (and is a bit of a mess, requiring files from various other projects including SBusFPGA and XiBus).