We have realtime grooming updates at our Telemark mountain cabin (see
http://www.visitrauland.com/Skiferie/Langrenn/Trac... ), the green is the big groomer (dual classic + skating in the middle) and yellow is a narrow (dual classic tracks) groomer.
@skitrails: Since you have a large number of track logs from each trail, I would assume that you can use some kind of (weighted) averaging to get the exact location of each of them, then you use the latest update just to select the color/type of line to be shown.
In the Lillehammer area they use this system, the only thing they are missing is the actual grooming timestamps.