I don't think its as outrageous as people are making out. He would be a fantastic signing as a central midfielder. Not only would he add AT LEAST 5k to the gate, he'd boost Rovers worldwide profile - and we'd get a lot more coverage in the press.
Advantages for Becks:
Huge Fish in a small Pond - he'd be THE star again - unlike at Madrid.
Guaranteed First Team Football - which he wouldn't be guaranteed at the Big Clubs
Close to Manchester - Can you see Posh living in Newcastle?
Sparky - Chance to play for one of his heroes
I think its unlikely - but a nice thought anyway.