We collected 16 bullet points worth of potential proposals and 2 of these matured enough to be seriously considered for inclusion in the specification. In the end, there was no consensus for accepting them among the authors of the 1.0 document. The specification will not now be revised and will stay at 1.0.
Ellipses and circles were not accepted because authors were not all willing to add a feature that would require knowledge and parameterization of the World Geodetic System for computing new latitudes and longitudes from distances measured in meters in the most common, no-CRS GeoJSON situation. Another concern was that the proposal couldn't provide any basis for representing semi-circles or products of circles, ellipses and other GeoJSON geometry types and that since consumers would be required to approximate them as polygons in most cases, why not just make them polygons to begin with?
The Data Series proposal struck authors as too far outside the scope of describing simple geographic features and as something that wasn't precluded by the current 1.0 specification.
Work on a 1.1 version has ended for now. I did my best to keep the process short and avoid burning people out so that we may start up again when the time is right. You can follow the entire discussion and consensus making process in the GeoJSON list archive from September, through October and ending in November.