For now, there isn't a plan to make Windstone Multiplayer, but that doesn't mean it could never happen. It really depends on the success of the game and how future development goes. I have built Windstone from the ground up as a single player game, so converting it to multiplayer would be quite an undertaking and would basically be like starting from scratch. Once the survival mechanics are fleshed out I am going to focus primarily on the story and quests.
For most of Winstone's time on itch, it has been free and will be free. I only periodically and temporarily put a price on it to help development but the increased numbers of downloads and exposure when it is free is probably more beneficial. If you download Windstone when it is free, you will never have to pay for it even when I put a price back on it as long as it's on itch. When and if it ever arrives on steam it will have a separate price, but I will be offering steam keys especially for those who have already paid for it on itch and even those who downloaded it for free and were helpful with feedback.