The discussion of the 1mB SRAM 'limitation' allows an interesting potential in terms of the open-source nature of the UltimateCart. Given we know exactly how the cart works, right down to the firmware would it not be possible to add a larger SRAM chip with similar electrical characteristics to the design? I guess that might introduce potential timing problems and the like though. It would be nice if you could simply remove the existing memory with hot air and then drop a larger replacement in place. I am sure it would not be that simple though!!!
You can purchase a e.g. 2MB SRAM for not that much more (a couple of pounds) than than the 1MB chip I used. It wouldn't be a drop in replacement, however, you'd need to route the extra address pin to a spare pin on the FPGA, then tweak the firmware in a couple of places. Not a big job.
EDIT - Santosp has reminded me that the 2MB version of the chip I am using is 3.3V supply only, rather than the 3.3-5V allowable supply for the current 1MB version. So you'd also need to power the larger SRAM with the 3.3V supply on the PCB, rather than the 5V as currently.
However, I just don't see the point, and the cart is already quite costly in parts cost. The SRAM isn't available to the Atari, it is simply used within the cartridge to emulate the whatever was selected from the SD card. And (megacart collections aside) there are no cartridges this big. A future firmware could make the SRAM available to the Atari through the CCTL window ($D5xx), but that would be a completely non-standard RAM expansion, so unlikely to gather much support.
Edited by electrotrains, Mon Mar 14, 2016 2:51 PM.