So based on reading the poem, Minecraft's poem is a play on the idea our universe is a hologram/simulation, which we the players are ironically enjoying simulations, the dream verse long dream. Not sure how much this ties into Minecraft's lore, but rather ties playing Minecraft to reality being a dream/simulation. In which the Poem's voices are arguable the universe or the creator(s) of our universe sneaking a message thru a simulation to the simulation. Or at least my best guess, probably missed the mark on it.

As for the Minecraft the game its more head lore, which there's lots of good and interesting ideas out there for sure. To start though I think the End is the place to begin.
  The End is limited in resources, and it's name suggest ominously its the final point of time and space, Unlike some theories I don't think Endermen are descendants of humans/players/villagers, but rather the last civilizations Golems. This would explain their behavior of only being aggressive if noticed an extreme guard function as nothing else in the game notices them, meaning what ever can is a threat of being able to travel thru time/space/dimensions for their creators. Their habit of randomly picking up blocks is left over/glitch of building under commands. This also explains why the End Cities are seemingly deserted, and there's no higher concentration of Endermen in Cities verses outside. So what happened to the End Civilization? Likely something to do with the Ender Dragon, my theory is that the Dragon was cloned by some faction in the End Civilization using Nether Stars to what purpose it's hard to say, but the Ender Dragon survived till the near cold death of universe where players encounter the End. I really enjoy the idea Shulkers are metamorphosed Endermites that burrowed into Purpur stone to mature, such a pest would be annoying in any civilization and golems/bots would be set to always take out such pests (for ease of life). Chorus reflect the diet and state of the End Civilization or is the last surviving crop at least of advance GMO of food that grants handy properties from their dabbing in magic.
  Enderman exist in all 3 dimensions (and if an more are official added probably them too [bonus to any mods that have Endermen in them in my opinion.) As Enderman's jobs are to preserve/safe guard time/space. This suggest the players are foreign entities which given default is nothing like anything else in the realms it's safe to say the player was somehow placed into the Overworld by some Time/Space/Dimension event. Which begs the question if any of the End Civilization escaped to the past/parallel are elsewhere avoiding dying out (or evolution back into the universe as suggested by the poem) the Endermen will attack, or possible defend.

  Now to the Begining, Nether, which has the source for the Nether Star and contributed to the End. I think the Nether is an earlier Time/Space point. For one the spacing suggest so with the 8:1 block ratio accepting and expanding universe. For this to hold true the End would in theory be an opposite, every 1 Overworld block would be 8+ block distance traveled in the End. However, I don't think that can be tested, which I would argue is because the End is so close to cold death there's a lost in the tangibility when traveling thru time/dimensions. The new Nether Update doesn't hurt this theory at all, given there will be fossils (dead dragons perhaps?) and Piglin seem far more primitive and aggressive compared to villagers, arguably early humanoids. Now what shifted the Nether to Overworld could be the cooling of the universe. In which as the Nether expanded its upper layers of bed rock folded slowly to the bottom like a ball of dough flattening out. Opening up and becoming the Overland. (Wildest part of my head theory but its for consistency.)

  Last but not least the Overworld, which is most similar to our own world, in both condition and arguable time along it's universe, somewhere in the middle. Not somewhere hot, hostile with bare bones of building blocks, nor spaced out too far for universal cold death.

  With all that said just my theory currently, I'm still rather new to Minecraft but it's missing lore does allow the imagination to roam, which is probably why they will never give us a lot of details. So we can build the story ourselves to some degree, and immerse more into the simulation within a simulation.