I was reading K.C. Joyner's section on the New England defense in his excellent "Scientific Football 2005," which I highly recommend, when I came across a passage that put the whole Parcells/Greg Ellis feud in a new perspective.
Joyner details the evolution of the 3-4 scheme from the Dolphins of the '70s through the Pats of the early '00s. According to Joyner the third major evolution, after the Parcells/Belichick Giants redefined the rush LB with Lawrence Taylor, came in the '90s when Steelers' DC Dick LeBeau redefined the roles of the 3-4 linemen. The Steelers had several undersized DL then and LeBeau adapted by using all of them, including his nose tackles, as cover men in the short zones. This made his pass rushes much harder to predict.
When Ellis' role in a 3-4 is considered the media and most of us on this site ponder how Ellis would function in a "pure" 3-4, where the front seven plays in static positions -- the tackles head up on the offensive tackles and the nose tackle over the center. Ellis' light weight of 271 lbs. is considered a liability in this formation. Joyner points out that the more effective 3-4s work because they avoid being this predictable. He is seconded by the writers at Pro Football Weekly's 2005 Annual, who note that most 3-4s these days are either "under" or "over" schemes, where the linemen "cheat" or line up over guards or in gaps. Almost nobody plays the plain vanilla 3-4 that Parcells' Giants used so effectively with Taylor and Carl Banks 20 years ago.
Ellis has already proven he can play inside in a 4-3. Dallas has been using him as a tackle on rushing downs for years. Given his intelligence and adaptibility, not to mention the adaptibility of the 3-4 as a scheme, perhaps Ellis should not see himself as the square peg in the round hole.