There is an OK way to do character swaps like that, and maybe they're doing it with Iron Man as it's one of the best potentials for it, of actually passing the mantle to a new person. Tony wants to retire, gets killed, do other shit, whatever... Keep the Iron Man legacy going with a new talent, but have that new person be their own thing as well. They've done that with Captain America like... a dozen times now, or something, right? Without any such outcry. I get going from Rogers to Bucky is more natural due to history, but that's not the only way those things can happen.
That all being said, I'm sure they'll do this horribly like they've done a bunch of other stuff horribly over the past couple years. I'm just saying it COULD be done well.