Good point, but I don't know if they'll go for it... Back in the 90's there were some Couture houses (Balmain, for example, but many more) with two designers, one for the HC and one for the rtw. That model ended because the identity of the lines was different and they considered it was sort of against building a strong, seamless image of the house. But times have changed, so... who knows!
And when Marc was at the helm of Vuitton, Julie did the precollections and got credit for it. Although, to be honest, every fashion house has a team for the precollections. Many people think the resort ones chez Chanel are the best KL does, but they are done by a complete different team. He just gives the ideas and a bunch of sketches and that's it.