I don't know if I'm misunderstanding it but when a new update is released you have to pay for it? If that´s true for someone that bought the game in itch.io can still buy the updates?
If you bought it on Itch.io or were part of the Kickstarter campaign, you won't have to pay anything else until the final update except if you want Beryllus when production finishes (who's only preowned for Kickstarter backers). Only for Patreon you have to pay for a new update.