Keeping combined threads going is nearly impossible. Everyone wants to be the first to start a new thread for a new car, then people start posting there and it usually sticks, so you end up with multiple threads.

The ONLY thread that I've seen avoid this was the "Schumacher Corner" thread, which managed to keep the same thread through about 7 different cars...but sadly enough, even that has split with the release of the Mi4...

...So if a thread that old, that big, and with plenty-o factory support can't' keep it altogether...theres not much hope for other threads.

Multiple threads for multiple cars from the same manufacturers are pretty much the way it is now.