Thank you very much :D! We will keep updating the demo to improve it and add more content here and there, but it won't be on a monthly schedule. I'd say an estimate would be every two months. Though possibly longer, depending on how busy we are with getting the game done. Making demo builds requires changing quite a few things so we can't do it all the time, sadly.
Our Patreon beta gets monthly updates, so that may be where some of the confusion comes from. Those builds are easier to do, since they don't need any special changes to make them right. It's just a beta version of whatever is done at the time, haha.
I hope that makes sense!