There is also the fact that a fight and film of this magnitude has to have death and consequence.
The universe-altering events in Avengers: Infinity War and Avengers 4 demand that every hero and their allies join in the fight for survival, so there’s a possibility that Pepper Potts could join this lineup.
While the retention of her Extremis powers is an open question, there is nothing stopping her from donning a great new suit built just for her.
If Pepper enters the fray to help or perhaps save Tony and is killed in the process, that would be a huge blow and give the battle with Thanos the appropriate gravity and stakes.