I've been playing this shit for years. I'd genuinely pay for this. Great game, honestly. Nothing really comes to mind when I think about what this game could improve on. Maybe more lore, a path to where we free elves (though I have a feeling this was intended anyways), more stuff and all. Or maybe some character customization (I personally dislike the hairstyle). But really, it's the high-end of how VN eroge games go. Not even playing it for the eroge at this point (though they are pretty good).
You can pay on Patreon and Subscribestar.
Paying on Itch.io is not possible anymore since last summer. That is due to campaign arranged by Collective Shout.