Thank you so much, I'm glad you're enjoying this and looking forward to what's coming up for it! There is a plan to include elements of slave training/play :)
Currently we don't have a precise schedule for future updates, and there's a very loose plan for the order in which content is going to be developed; there will be more details available on the Discord server when it's launched (currently in the process of getting it set up).
Each game update will have a free demo and a paid demo; if you want access to the content in the paid demo game files, then yes, you'll need to pay again when the game is updated.