Omnibus are expensive items and are only produced for famous characters and authors (the only exception has been TOD and Howard but I think these were planned in part to help Gerber and Colan who had medicall bills and even so, Dracula is a famous character and Howard was one of the first Marvel characters to make it to the big screen)
Based on this I think we can expect the following:
Thor Omnibus when the movie comes out (most probably Kirby because Kirby is a proven seller but Simonson and Jurgens/Romita Jr would I'm sure sell easily)
Daredevil by Nocenti/Romita Jr. Nocenti wrote the best DD story of the last years in DD 500, Romita Jr continues to be a high-profile artist, Williamson who is now retired got an Eisner, and since DD has the most omnibi already, readers are probably ready for the only remaining uncollected great run.
FF by Byrne (the Visionaries editions are inadequate, there are issues in them which aren't welcome like Avengers 263, X-Factor 1, even Secret Wars II is dubious while The She-Hulk graphic novel belongs with it in addition to being the right format for a GN)
Since there is an upcoming Avengers movie, an Omnibus should be planned but has there been a great 30 issue run with bankable creators? I'm afraid the most bankable author is Bendis. I'd prefer Thomas/Buscema (Avengers 55-85) or Englehart (too long), Michelinie/Byrne/Perez (too short), Busiek/Perez
A JMS Spider-Man Omnibus is a good bet but unlikely given the current ultimate edition.
Given Claremont/Byrne's prestige for Uncanny, their MTU or Iron Fist work would be good.
A Ditko Dr Strange Omnibus (including ASM annual 2) is in order.
Another Ennis Punisher is another good bet.

Personnally I'd like Killraven omnibused but that's not gonna happen. Untold tales of Spider-Man (AF 16-18, UNTOS 1-25, An 1-2, Strange Encounters) is another unlikely Omnibus i'd like (Williamson was nominated or awarded for his inking on this). X-Force/X-Statix by Milligan/Allred