Carmine lived upstairs anyway, so Shirley could've dropped into Laverne's apartment every day without a lot of plot restructuring. They would have had to limit Cindy Williams' physical comedy, but Lucille Ball made it work.

would have been cute huh?

I wish they'd gone through with it, since they were already planning on turning the show into a couples' program anyway, with Shirley and Laverne as married neighbors with kids (the plan was to marry off Laverne to Larry Breeding's Mike Bailey, which sadly didn't come to pass due to Breeding's tragic death). David Lander went on the record that it was the best possible solution to the situation. But they were holding out hope the Carmine spin-off would fly. It did not.