As I started watching Touring cars in the mid-90's 'proper' touring cars will always be 4 door saloons and 5 door hatchbacks (Mondeo). The BTC-touring formula was based on smaller cars than Mondeo's, 320i's, 406's but larger cars than Focus's, Meganes etc... Therefore alot of manufacturers didn't have a car the right size to race so it was always going to fail
However I can't see the WTCC being a long term success. I think that TOCA and Alan Gow know more about running successful Touring Cars than the FIA does.