Started to see more of this last year. A local pumpkin beer was on tap at most of the beer tents (I forget the brewery), and most tents had a local selection on tap mixed in with the AB products. I want to say Transformers pop-up bar had the best selection, but obviously subject to change.
Dufftoberfest is the best of the four Duffs, tho all of them are good. Don't forget Diagon Alley has two local beers on tap as well, a stout and a red.
If you don't mind a short Uber ride off-property, consider a visit to Yardhouse (by the Ferris wheel) or Player 1 Video Game Bar. Both are close, have very large beer selections.