I agree with the first paragraph of what Bondage Queen said as it's been a long time since you last worked fully on Mira Co Rescue and with the fact that you haven't had a game design document made up will mean it's going to be hard enough making sure it's all wrapped up, let alone add more on to it.
For your next game as I'm personally not for MILF's I'm not for then them being the main focus of it. However it will be your game, your project and thus you whom should be in control and deciding what happens with it. No point in starting a new game with a setting you hate or aren't on board with. Although how well a continuation of Mira Co Rescue goes depends on how you wrap it up otherwise Camo or mention in conversation or newspaper of sorts is probably best to do at most in the next game.
Something you should do with the next game when making the game design document is consider if RPG Maker is the engine you want to use still or not and look for other games that have done similar mechanics to what your wanting to do. E.G in-depth bondage escape system like Didnapper series has.
Hope this has helped.