I don't know if it's embarrassing, Vrabel may well like his situation in Houston and may want another year or two as a LB coach before he moves up to DC on another team.
I'll say this about Jim Schwartz as DC in Philly. He was a great pick and I always loved the 4-3 defense he ran. I've always been a 4-3 defense guy, but I'm not sure how often he'll run the Wide 9 defense DC Gunther Cunningham ran in Detroit.
The key to the 4-3, or any defense really, starts with the defensive lineman. They don't have the talent Schwartz had with Suh in Detroit or Marcell Dareus in Buffalo. That talent is necessary to get to the QB and cause defensive turnovers, which Schwartz's defenses do, and I don't know if the Eagles have that.