I love what Markus & McFeely have written for Cap, I love what the Russos have done for him as directors. I am over the moon on how fantastic Chris Evans is Steve Rogers.
There is nothing the creative team has done that shows that they don't respect and love Steve Rogers and consider him the star of his own show. There is nothing in what I've read about the upcoming movie that I expect to change that.
Adding Black Widow as an almost co-lead, adding Falcon as new friend/superhero and having Bucky return from the dead all tortured and bad-ass took nothing away from Steve as the center of his film in in TWS or detracted in any way from Evan's magnificent performance. They all just gave him new elements to play off.
I expect nothing different in regards to RDJ's Iron Man or Chad's BP or anyone else added to the film. Steve will still be front and center and the film will still be about how Steve affects and changes the world around him.
Tony has always been a big part or Steve's life in the comic, professionally and personally and there's no reason that should be confined to just the Avengers. The Civil War while it messily sprawled across the entire Marvel universe was at it's core about Steve and Tony.
It's obvious from that clip of them shown from AOU that this story is being built to and that this film will also have repercussions to the MCU - just as TWS did.
So much of the kvetching I've read about this online from fans is worry about how his supporting cast will get less screen time, mostly about Bucky. Frankly I'm not concerned. They'll get enough to flesh out their characters and relationships and tell a bit of their story. M&M and The Russos have shown they can work well and in depth with multiple characters.
But in the end this isn't a Cap and his Crew story and certainly not a Bucky Barnes movie. It's a Steve Rogers movie. He is the main protagonist and every other character in the films exists to play off or affect, be it Bucky, Sam, BW, Fury, Peggy, Erskine, The Howling Commandos, Red Skull etc. I don't expect that to be any different with Tony and T'Challa.