Couple thoughts...
The Nations would love Denard Span to be their table-setting CF. Bernadina and Nady would be expendable to them if they had Span and they'd have no problem letting go of those strings. The Werth injury could spurn the Nat's to move more quickly, but there interest has to be very high regardless. The Nat's are adequate without Span, as Ankiel is decent enough and they are ok with Tyler Moore to get reps in place of Werth, but they would be far happier with Span.
Jordan Zimmerman is off the table... just forget about that. The Nat's have not and will not give up quality young pitching that is extremely useful in their current pennent drive... has any team ever done such a thing? One problem with the Nat's is the Gio Gonzalez trade... the A's took most of what the Twins would have wanted for Span, so there is not much left to pick from and like another poster mentioned, what is left may not be trade elligible until after this year's draft (although that 1 year rule has been known to be waived with a simple request).
Having said all that, I could see:
Span for Daniel Rosenabum & future considerations (Anthony Rendon)
Not the type of deal I'd usually see from the Nat's, but their M.O. has changed now that they think they can win now. IMO.