They are using Media Composer on The Hobbit and that is one of the films I was loosely referring to. Because my involvement with their pipeline was when I was still with Avid, there was an NDA in place I am respecting to not disclose actual pipeline, etc. until they do.
As it is obvious by the need, there is a conversion from 48fps to 24 by transcoding every other frame. One could make the assumption that there is some consistency put into place for the metadata tracking back to the 48fps, such as keep all even or odd timecodes in the proxy files, while maintaining the "Original Start" timecode in the database to know whether the clip started on an odd or even timecode. The reason I asked RED to make the START redundant in the ALE file several years ago was because the Avid bin is its own database, but the clips can change over time with transcodes, handles and the such. By maintaining the original start in the file, it can always be used as an anchor point into third party databases - and in this case, the flag to whether the proxy file being used is starting on frame 1 or 2 of original camera file. And of course, double the metadata for LEFT and RIGHT eye management... ;) Actually more than double. There the set of metadata for left and then right, then stereo 3D specific metadata that relates to the relation between the two. MC v6 stereo 3D feature set was designed by Steve McNeill to support all these types of relationships of the original sources and the association of the two or more clips when managed as S3D.
But as far as The Hobbit is concerned, that is all I can say for now.