The biggest bombshell is that the console will allow you to use your original carts thanks to interchangeable modules, very much like the Polymega – with the obvious difference being that it will do so via FPGA emulation rather than software emulation. This update has required the team to completely redesign the console's physical case.
The modules will have their own controller ports, so you'll be able to use your original pads and accessories as well.
It has also been revealed that MARS will support a bunch of legacy AV connections, including S-video, Component, and RGB.
As for an estimated launch window, the MARS team says they will have a better idea of that "in the next 6-8 weeks."