After watching the new trailer that aired tonight I have a theory on an early Avenger death that will spark both an emotional reaction from the team and also contribute to Tony being driven towards registration.
I think Iron Patriot is going to die, and relatively early in the movie.
The more I think about it the more it makes sense (to me at least). There arent anymore Iron Man movies slated for the Phase 3 and most likely Iron Man 4 will be recast and somewhere around 2021. So of all the marvel movies coming out I dont see a strong need for two "iron man type" characters.
Next, Iron Patriot being featured prominently in the trailer (but never in armored form) seems to be an attempt to build an attraction with the audience and hence receive a reaction at his death. I think this will lend to Tony being a slightly more sympathetic character who feels his death may have preventable if registration were in affect (somehow), and it will create a more dichotomous effect with the audience where some may agree with him since his best friend was just killed.
Just a theory.