Right now it is indeed a subscription. You pay for that month's content. If you stop being a Patron, you won't be able to get any new content. You're still able to play the content you've pledged for, and in the future if you want to re-pledge, the game will update for you with new content.
It's basically a way to personally support me and get early access to the game :)
The Tailor Tales Plus that will get released on itch.io (sometime) will be a one-time purchase, and you will always get new content. Right now, I have no date set for that version.