Maybe everyone interested should write one story with just another superhero?
I, for once, would like to see Martian Manhunter on a date with Lois. What would he think - if he ever picked up on some of her thoughts? Or the Flash? Always running off for milliseconds, only a gust of wind giving him away? Or, come to think of it: Booster Gold? Blue Beetle? Ironman? Thor? The Human Torch?
As you can see, I don't think it's a sin to write a Marvel/DC crossover. Not since I read an official JLA/Avengers crossover which happened to be excellent.