Before starting, note that I haven't really read much of the discussion so if this interpretation already exists then feel free to link it - I'm basing this off of my experience playing and the steam store page of the game. Enjoy!

So, the first and most obvious thing to notice is that its called "A Raven Monologue" despite Sir Raven talking to multiple people throughout the game. Which is strange, right? It doesn't really add up since the definition of a monologue is someone talking to themselves. We also notice as the game continues, those people Sir Raven met, when he returns, either become rocks (implying either the humans grew old and died (though its a bit more symbolic than literal)) during his journey or were always rocks that Sir Raven projected on/hallucinated, which means they never truly existed.
I personally believe the former: that the humans were real and did die during Sir Raven's journey. I'll explain why in a moment.

The second thing I noticed was this poem on the store page:
"Dearest Sir Raven, / Do you still wander around without end? / Crafting colors under the still and silent / Not knowing I'm waiting here alone without a friend / Dearest Sir Raven, / When you are around, would you mind to stop by? / Just a hello, just a moment / To let me savor the memories before our goodbye / Dearest Sir Raven, / Let us go home / To the place devoid of reality frame / Where I shall watch over us even without a logical form"
I'm unsure who is speaking, maybe the pinwheel girl, but I'm far more interested in the lines "Do you still wander around without end?" implying, pretty obviously, the Raven can't die and is searching for something.
"Crafting colors under the still and silent" still and silent is a very clear reference to people who have died; this is partly why I believe the humans were alive and then died during Sir Raven's journey.
I don't really have any idea what crafting colors means, maybe its a reference to the items? They do stay colorful even after the world has faded to black and white at the end of the game. Prior to when they dissipate, of course.

The last thing I noticed on the store page was the description: "A Raven Monologue is a short experimental silent story about a raven that does not know how to croak and his relationship with the people in the town."
This implies two things.
First, in the line "about a raven that does not know how to croak," is outright saying Sir Raven doesn't know how to die. Raven's don't make a croak noise, but croak is slang for dying.
And then the line "his relationship with the people in the town" implies the people are real and do (or did) exist and not that they were a hallucination by Sir Raven.

Lastly, let's talk about what Raven's tend to represent. And while I didn't look all that deep and I'm sort of blindly trusting Wikipedia here, I am going to quote it lol
"Because of its black plumage, croaking call, and diet of carrion, the raven is often associated with loss and ill omen ... As a carrion bird, ravens became associated with the dead and with lost souls."
And while, whether you trust Wikipedia, or not, I personally believe this interpretation of loss, ill omen, the dead, and lost souls is very intentional.

With all that in mind, let me tell you my interpretation:
I believe "A Raven Monologue" is about an immortal raven that meets and receives items from people in the town. Along his journey his friends all pass away (become rocks).
This is why on subsequent playthroughs the people don't come back. They stay rocks; they stay dead. The raven repeats his endless journey to see his friends again, but he can't. He can only receive the items, which I interpret as metaphorical representations of his memories of them. And when he returns home, they fade away; just like our memories.

Sometimes it's hard to remember people we've lost until we return to a trigger: an item, a place, a smell, a song; then we remember them in a very powerful way, but inevitably it will fade away.

And yeah, that's pretty much it.
It isn't a perfect interpretation. There are probably some holes and I'm sure the song that plays would shed more light on what the developers intended. But, this is what I think.
I am interested if anyone else came to this conclusion or think something else though, this is a pretty cool game and I love abstract, theory craft-y stuff like this.