Yes, buying the game on Itch gives access to all future updates for no further cost. Patrons still get early access to new updates for now.
Once the game has a finale and leaves its early access period, I plan to open the patron features to everyone (mostly the ability to Reminisce previous scenes) and publicize the cheat menu password.
I don't currently have any plans for paid expansions/DLC. I can imagine a world where I charge for some sort of chunky story expansion, but it feels unlikely.