And did they ever do this? It sounds so canon, like the lighthearted subplot in some episode that was serious for other characters, when Justin/Brian were a little boring because their relationship was smooth sailing at that point :-D
And although I know they're less sexy, I could see Mel and Linds doing this too, at one of those magical stages where their relationship was reinvigorated and sorted.
I would love to try this one but it would probably take me about a year and remedial therapy of some kind to be able to figure out a plot :D