SHIELD will have some sort of presence in any Iron Man movie I think. Whether its a physical cameo from Coulson, Hill, or Fury, or there is a computer screen or paperwork with the SHIELD logo, it will be there.
I would hope they keep IM3 all about IM and leave the other big-time heroes at home. I wouldn't be surprised if War Machine had some part in it, but let it focus on Stark and his enemy for this film.