We have not deleted the MarlinDev repository yet. But it is inactive. The people contributing regularly to Marlin do not want to go down the 'Customization.h' path because it would force them to abandon all of the code forks they have. There are strong arguments on both sides, but the people actually contributing want the code structured the way it is on the MarlinFirmware/Marlin side.

With that said, we have started a Development branch and we do expect to promote RC-6 to RC-7 very soon. And we expect to promote RC-7 to a Stable v1.1.0 release. RC-6 is pretty solid. If you are loading up a new printer, it is a good firmware to load.