Yes, as a matter of fact, that is exactly what the Lions would do. If BPA were a WR the next 8 years in a row, they draft him.
BPA is not just a philosophy that pertains to filling holes in the draft, and Mayhew said so three years ago. He said you can never have too many good players. He also said if you have three really great QBs, then you have one or two that can be traded to another team for the players you need, because another team will always need a great QB.
Obviously not a direct quote, it was three years ago.
Point is, yes, adding a fifth very good WR would allow us to potentially trade one for a CB, and at the same time, keep our WR corpse young.
It's the very reason why I say BPA is BPA... if we get to our pick next year in round one and BPA is a QB, we take him. If it's a DT, we take him. And if it's a WR, we take him. Then lets see who needs a QB, a DT, or a WR in those cases and lets the trades being.
For a lot of these guys you might have to hold onto them for a year or two and let them prove themselves, but consider what the Cardinals gave up for Kolb, what several teams were willing to give up for Flynn, and what Texas gave up for Shaub.