Patreon rewards are always a difficult thing to ponder about for most people, in all sorts of mediums not only for game creators.
I don't personally like the idea of an early release date, not because of some sort of injustice towards smaller patreons, but because it would be easily circumvented by a leaker.
If I had to chose any possible rewards for higher patreons, it would be a monthly release for every patron, a small animation like it was the case for those extra scenes that Sekai Translations included in their patch, and pictures with Inoda's blog style writting to accompany them of non-canon or bonus content.
All that decided for by a poll the previous month with low tier donors (5 dollars) having 1 vote and high tier donors (10 dollars) having 5 votes.
An example of that, it would be like seeing Asuna drink the cum latte that Inoda delivered to her or something like that.