Yeah, I totally feel like staying a woman should be a choice in the hidden ending, because that does seem to be a reoccurring option in most of the content of the game, so it makes sense to at least let it be an option for the player to pick.
Edit: One thing I did also find surprising with the hidden ending, is that Frederick decided to go back to being a guy as well. I haven't seen every ending yet I'm sure, but he does seem to pick staying as a girl a whole lot, so that surprised me a bit when he turned back in the hidden ending. Nothing is wrong with that mind you, it was just a surprise to see. I would love to know what's different in that path, that makes him make that decision compared to the endings where he stays a woman. Especially when he does seem to enjoy being a woman.
As for new content, take however long it takes dev. There's no point in rushing it, especially if it isn't content that appeals a ton to yourself as a person. Trying to force yourself to write something you don't enjoy as fast as you can, will only make it a bigger challenge to write it. As for myself I'm more than contend to wait for it to be done, and whatever time it takes is worth waiting. I might try it out in the increments that you end up releasing it in, or I might wait for it to be done, but we'll see. Either way, I don't mind it.
I'm excited to see what the RPG maker game is about though! I've pleasantly enjoyed almost every other game you've released on TFGs, so I'm excited to see whatever this next game is about! I'm curious about the visual novel version though. I assume it doesn't change much plot-wise to what we already have, but how much is the different transformations on display in the game? Does the MC have a sprite that changes as well, or is it a 'first person point of view' sorta situation, where only the other characters have a sprite? I might just try it out later today when I'm done with my chores for the day.