Currently we resolve grid-{row|column}-position 'auto' as meaning the (1 1) grid area. The specification defines a placement algorithm that is controlled by 'grid-auto-flow'.
The implementation of the main algorithm is done. I am keeping this bug around to track some open issues in the code / specification.
Auto-placement implementation has been completed and it's now following the last ED: http://dev.w3.org/csswg/css-grid/#grid-auto-flow-property So, I guess we can close this now.