This might be a tall order, but if it is possible, I could see it becoming a bestseller.
Hornby should make a 3-pack of GWR Slip coaches that have special electromagnetic couplings that actually enable the coaches to detach from the train whilst still running. These couplings could be operated by a basic DCC decoder.
Just imagine running a slip coach train on your layout and having the ability to detach any coach you want at any of your stations.