Just a couple of things.
1. I think we can stand down on any concerns that a power conference team or Wichita State (or VCU, who can't play Duke anyway) will fall to a 12. There are no longer any power conference teams listed as 12s on the bracket matrix, since one-bid leagues now fill every spot from 12 to 16 as well as an 11 (most likely UALR). It's somewhat likelier, though still really unlikely, that Duke would drop to a 6. If so, everything is on the table--this field has about a dozen teams that are plausible 11 seeds.
2. There are four plausible first round sites for Duke as a 4-5 seed, since Raleigh/Des Moines/St. Louis/Brooklyn will all be taken up by teams seeded 1-3. If Duke is a 4, my hunch is they would get Providence (based on geography) or Denver (to help fill up the 19,000 seat arena). If Duke's a 5, then they go where the 4 goes: Providence if it's Maryland, OKC if it's TAMU, Denver if it's Utah, etc. I don't want Denver--the thought of Marshall playing his 35-40 minutes at high altitude is awful.
3. Some people are talking about Duke being in UNC's region or Virginia's, which I guess does not violate any bracket principle, but it seems highly unlikely to me. That leaves only Kansas' Midwest region or MSU's West region. So I would say it's like an 85-90% chance Duke is a 4/5 in the Midwest or West, with 5 way more likely than 4.