I don't disagree with RGS5526 but it's just not good business. BA currently have the best of both worlds by selling as much CE as possible knowing they can accommodate the PAX in a flexible configuration. (other than the lost revenue from the middle seat, I'm guessing the CE soft product costs BA around 20 quid for booze and food, and saves fuel / increases the freight which can be carried. Limiting club to 4 rows would merely bump up the price(the first economic rule you're taught of supply vs demand and the effect on price.
However, I do think there should be a cap on the rows as club. My best friend is a SH Purser on BA, and talks about the challenge of a full service on a short flight where BOB trolleys are at the front and delay service. There is a fine line between making more money from club, and deterring PAX from buying it for a short flight if it then becomes a lottery on the quality of service based on the size of the cabin