Some of them might be shocked. Tony Stark, for instance, might immediately start thinking of ways to use technology to change what he saw. Steve Rogers would probably be more concerned about the moral implications of interfering with the future.
Well, they might see a lot of different things. Maybe they'd see new threats emerging and start preparing for them right away. They could also see changes in their relationships, like friendships turning sour or new romances forming.
In most cases, watching (reading) fanfiction is legal as long as it doesn't violate copyright laws in a major way. Fanfiction is often a derivative work, and as long as it's not being sold commercially without permission from the original copyright holder and is more of a non - profit creative exploration of existing works, it's usually okay.
Some characters would likely be entertained. For instance, Loki might enjoy seeing the various ways fans write him as a more complex anti - hero. He'd probably find the creativity in the fanfiction quite appealing.
Future Loki might interact with the Avengers in a cautious way. He knows their past opinions of him and tries to prove himself. He could start by sharing small bits of useful information. For example, he might tell Iron Man about a weakness in a new enemy's technology.
One of the great platforms is Archive of Our Own (AO3). It has a vast collection of Avengers fanfiction. Another option could be FanFiction.net which also has a wide range of stories. Wattpad might also have some interesting Avengers fanfiction, although it has a broader range of content in general.
I think Levi could benefit as well. His combat skills are already top - notch, but seeing the future could help him anticipate enemy attacks even better. He could train his squad more effectively based on the future battles he witnesses, ensuring their survival and making them even more formidable against the Titans.
Well, it depends on what he changes in the past. If he stops certain villains from emerging, the future of the Avengers could be one of relative peace. They might be able to focus on more positive things like exploring the universe or helping humanity in a more proactive way. However, if he changes things in a way that disrupts the natural order too much, it could create new and unexpected threats that the Avengers are ill - equipped to handle.
Maybe they're just bored. After all their battles and saving the world, they need some entertainment. Batman fanfiction could be a new and different form of it.