The Sentinel-2 geometric calibration team is still actively working on the preparation of the geometric refinement. The prototype processor has demonstrated long ago the efficiency of the geometric refinement for Sentinel-2 images. However the transfer to operations has proved more difficult than anticipated. First, the verification of the Global Reference Image (4 TB of data and millions of files) has taken more time than anticipated. Second, we had to rework the processing algorithm to make it more accurate and more robust. We have made some decisive progress recently and it looks like we will be able to activate the geometric refinement early next year.
Regarding the reprocessing of the archive, it is yet another story and ESA does not yet have any planning for this as far as I know.