I think that improvements to the AGA chipset performance and features (including higher resolutions and color depth choices, as well as the ability to access greater than 2mb of Chip RAM), by using FPGA chips
Out of curiosity, how would this work? I know this is basically how the IndivisionECS works, by replacing Denise with an FPGA (and from what I understand, the ECS model is actually more advanced than the IndivisionAGA, since the ECS can operate without the Denise chip entirely)... but since most AGA chips are SMD, are you proposing something like a "super IndivisionAGA", that would graft onto the top of the AGA chips, hijack their signals, and enhance them? Or something entirely different, that might fit in the video slot of big box Amiga's? Just trying to wrap my brain around how this might work.
