What would be your ideal “Will having powers” outcome for season 5?
I don't really like any of the theories about him being in the lab as a kid and repressing those memories because I like the idea of him being a random kid kind of thrust into power rather than being born with it. I'd like it if it was based on his whole hiding thing from S1 where he manifested the Upside Down into Hawkins and/or blipped himself there subconsciously to escape the demogorgon. I like the idea that it's an accidental coping mechanism more than a super power if that makes any sense. Him blipping himself to the Upside Down due to trauma could also relate to S2 and his PTSD, although I also like the idea that the blips were because of his mental link to Vecna (perhaps via tentacle).
In terms of a reveal of this, I imagine it would be Vecna in S5 trying to get Will to join him or at least mess him up mentally where he'd have some sort of "we're more alike than you think, William" reveal, showing that Will was actually holding a lot of repressed power inside of him. And then Vecna could give him a whole spiel like he did to young Eleven about society not being able to handle people who are different and powerful and how great he and Will could be together. We could see clips of the past with Henry and Will parallels, the mind flayer and Will saying the mind flayer wanted to kill everyone except for him before he was even flayed. Remember, they did say S5 is based off of a scrapped S2 concept and that Will was at the center of it.
However, after this reveal Will would instead reject Vecna because Will is not like Vecna. Vecna became bitter because of societal rejection but Will through his love (not just romantic) and kindness was able to accept himself regardless of what others thought and try to use his feelings for good. Would Vecna have given a crying girl his toy even though he couldn't afford a new one? Would he have made a painting for someone but lied about who commissioned it because he thought it would make them happy? No way. Because the parallels between Will and Vecna were not because they're alike; it's because Will is the opposite of Vecna. (@paladin-n-cleric has a brilliant post on that if I recall correctly).
At the end of the series, Will would help defeat Vecna but instead of destroying the Upside Down or himself, I like the idea that Will frees the Upside Down. The Upside Down being frozen in the past represents how Will is stuck in the past and in his childhood. However, instead of destroying the parts of himself he doesn't like such as his powers and his links to the Upside Down, he's able to reclaim them for good. I kind of like the idea of him being the peace keeper of the Upside Down but I also like the idea that after he comes out and/or uses his powers, the Upside Down becomes either the present or as it was before Will; an empty abyss where creatures are able to roam freely and separately from our world. I say and/or because this is could be a gay metaphor or a childhood trauma metaphor or both.
Don't know if this makes sense, thanks for the ask anon (: