My current understanding is that if you’re selling the game for less than it is on Steam on a different storefront, you’re not supposed to provide Steam keys. I really like the idea of being able to pay less to skip getting a key – I just haven’t every seen anyone do it or talk about it.
I have been advised to not play too many games with schemes like that because you want to stay on Steam’s good side, but who knows how much of that is hearsay.
Another possible option if we want to keep the price low here is “grandfather in” everyone who’s already bought it on itch before it was available on Steam, but not provide more going forward. I think it is an important priority to make sure people don’t have to buy it twice if they got it early, whatever form that ends up taking.