Avengers 4: 10 Rumours We Hope Aren't True
4. Somebody Comes Back Evil
No doubt the purpose of Avengers 4's time-jumping escapades is to reverse what Thanos did to the universe in Infinity War. The heroes could be about to create an alternate timeline, and that always comes with huge ramifications.
Performing a hard reset on the Marvel Cinematic Universe would leave it forever changed, and some characters are unlikely to be the same as before. How they might change is open to speculation, but some of the online chatter - echoed here by CBR - seems to suggest a number of fans believe a hero or two could return from the other side evil.
Prime candidates for this treatment would be Bucky and Scarlet Witch, given that there's a chance they could revert to past versions of themselves. Hopefully, this isn't the case, especially where Bucky is concerned. It wouldn't exactly be fair to undo all of that mind reprogramming the Wakandans worked so hard on.
Moreover, the whole 'good-guy-gone-bad' thing has been done to death and has already been explored in the MCU when Hawkeye found himself under Loki's control.