If you look back over the past couple of years, big patches seem to come out at approx. 6 month intervals (this is why I personally expected one about now).
There also seems to be some sort of pattern with the smaller patches.
We get compatible updates with backend improvements and some graphical niceties.
Then we get something that is multiplayer incompatible.
Then we get something that is physics incompatible and requires a reset of hotlaps etc.
With the latest test patches, I think we are at the first step above.
It was stated that fixing the LX4 numberplate glitch would make it physics incompatible, so I guess we'll have to wait until the next 'big' patch for that, and hopefully some more updated interiors. Also, adding a whole new car wouldn't cause anything existing to become incompatible.
Just my take on things...I could of course have the wrong end of the stick, or be in completely the wrong forest