MytimetoShineHello is one of the most reliable sources when it comes to the MCU, so I won't be surprised if this one is also true. However, it is a weak angle for an Avengers film revenge plot for me. I'm still waiting for a Thanos-level villain, and a faceless Doctor Doom looking to kill Steve Rogers because of some accident just doesn't cut it for me.
I'm really worried that Avengers Doomsday will be a huge disappointment, but I'm still hopeful. I hope there is more to Doom's mission when the film is finally released.