Thanks so much for trying our demo, and glad that you enjoyed a2 as well! The Pirate Mermaid was approved on Steam Greenlight a few months ago, so we are definitely putting it on Steam once it's complete. Feel free to follow the game on Steam here if you want to know when it's released.
About whether the full game will be PWYW, we’ve been thinking about offering both a free/PWYW and fixed price version. The PWYW version would be simpler and shorter (for example, no voice acting, no hint system, fewer routes/endings, etc.), whereas the fixed price version would have more features and content. We’d honestly love to make everything PWYW like a2, so that more people could play it. But at the same time, we really don’t want to go broke, else we won’t be able to make more games in the future. :’D
Thanks again for your support, and hope you enjoy the full game once it's out!