Britt has looked like the worst WR in the NFL all year long. He's a major character risk, so I don't think anyone would be happy if the Lions made a move with him. Especially if he did something that resulted in messing up team chemistry or getting suspended.
Josh Gordon is an awesome WR who's coming into his own, but he's a character issue of a different sort. He's one failed drug test away from a year long suspension. And, although he may have the talent to help take the Lions over the top for this season, if he decides to get a little too party crazy in the offseason again then he will have screwed the Lions offense for the next year.
It's too bad there aren't many WR who could be dealt to the Lions this year, but I think the team will be looking good late in the season as Burleson gets healthy and Broyles gets more targets. I think the plan all along for Mayhew has been to look to next years draft and scoop a height-weight-speed, game changing WR. But, who knows!