Okay, so long before "The Avengers: Age of Ultron" came out, there was an animated movie about Ultron called "The Next Avengers: Heroes of Tomorrow", which for those who haven't seen it, is after the original Avengers fight Ultron and lose. Then, the children of the Avengers- James Rogers (Son of Captain America and Black Widow), Torunn (Daughter of Thor) ,Henry Pym Jr. (Son of Giant Man and Wasp), Azari (Son of Black Panther and Storm), Francis Barton (Son of Hawkeye) are taken care of by old Tony Stark and later assembled to become the "Next Avengers." This is a time way into the future where Ultron beat the Avengers and made a city in his image.
When "The Avengers: Age of Ultron" came out, I was expecting Ultron to be exactly like in that movie; scary, soulless and able to beat the Avengers with ease. The I left the movie theater heart-broken and confused. I was expecting Ultron to be like Dr. Will Caster from the movie "Transcendence," to be a quick leaning and adaptive conscious based program that turned every piece of technology on earth against the Avengers. By the end of the movie, I left thinking two things. Ultron was severely under-portrayed and why didn't Thor see the two missing Infinity Stones in his vision? All the infinity stones in the MCU are accounted for except the "Time Gem" and "Soul Gem". The "Soul Gem" is most likely being introduced in Doctor Strange, November 4, 2016, as the "Eye of Agamotto," so the only infinity stone unaccounted for is the time gem.
What if Ultron actually won
Maybe Ultron didn't suffer defeat but by some unknown, or even known, character he was tampered with to have a different out come, like in "X-Men: Days of Future Past" and "Justice League: The Flashpoint Paradox." Somewhere deep in the future, long after Ultron won, someone used the "Time Gem" to go back and rewrite history.
I know what you're thinking. "Wouldn't it be easier if they changed something before the birth of Ultron to prevent him from ever being created?" "Is the person who used the stone going to use it against Thanos?" To answer the first question, maybe the person who went back in time kept changing history to get it just right. And to answer the second question, that might be the way "The Avengers: Infinity War Part 2" will end; with the "Time Gem." The mystery person could have it, lose it, then retrieve it. Looks like we'll find out on May 3, 2019 (the day after I turn 22!)