Couldn’t you at least keep the downloadable files available?
The problem is that the itch version is older than the one in Steam (1.2.3_EA). I am requesting Keys to Steam to be able to send it to those who want to migrate to the Steam version, for this they must send a proof of purchase to the discord server in the support area.
I don’t think it’s fair to keep an old version which doesn’t have the updates like a new parallel ending or some extra features.
Maybe tag it as “deprecated version” or something? Not requesting for the game to be relisted, just that it isn’t removed from the accounts of people that got it. And while the Steam key is appreciated and Itchio isn’t popular like Steam / GOG / EGS, I would presume that, if someone gets a game here, they had the intention of having the game here, not elsewhere.
And regarding having an older version, on a more personal point, maybe I’m on a nicher side, but I like to play old versions of games, even if they’re incomplete.