I spent the last two days implementing a rudimentary Sega System 1 arcade driver. By rudimentary I mean I haven't completed all aspects of it (including adding System 2 support), but for the most part it's fairly good at the moment
There is scarce information about this arcade system out there. There is a MAME driver, but it has a few bugs here and there that RetroCopy will be improving upon. I'm not going to bother going fully cycle accurate with this driver as there is F-all information about the VDP (graphics processor) and I have no System 1 boards to test on.
Given all that though it will be the most accurate way to play the System 1 games when released because it has cycle accuracy in the Z80 and sound unlike MAME, whilst also being a bit more accurate with the video too.