I don't think they can get Coulson too involved with the crazier stuff in this movie... As in, he shouldn't be exposed to too much in this movie, or else it might contradict his appearances in Agents of SHIELD and even the Phase One films. He can't see too much (especially with Kree or Skrulls) or you'll be wondering why he didn't mention that stuff later.
Yes, I know Feige "doesn't care" about AoS or what the movies might do to make them irrelevant, but I honestly believe Clark Gregg wouldn't have signed on for this movie if he thought it'd basically contradict his Coulson on AoS.
But I'm sure that AoS will let Coulson acknowledge its events after the movie releases (if the show even lives on for another season). It could be their most interesting semi-crossover of the MCU films to date.