Honestly, @Awesome_Lensfun1, between how long it takes to set up a plotline like the MCU so far, actually filming it, THEN executing things without messing them all up AS WELL AS studio rights ( glares at Sony ), I doubt that half of that stuff will make it past the movie-theorist line.
Deadpool probably won't be killing everyone like that comic series (which was horrifically violent btw...) unless it was an animated series like the Hulk and Black Panther MA mini-series.
Secret Wars, IF it actually going to happen, probably won't be as massive as Infinity Wars (see how it sounds like a copy of it?). So, if anything, it'll be a side plot for some other Phase 4 film just like how the whole Planet Hulk storyline was stuffed into Thor: Ragnarok without a second mention.
Galactus? ( glares at Sony again ). But yeah, he's a real possibility if they bring Silver Surfer back into the mix, which i really hope they do. You might be onto somethign here as Disney has recently obtained A LOT more rights into that stuff MCU-wise.
You know what I really want to see? Amatsu Mikoboshi, but I really doubt that the MCU's ready for that haha.