Thanks for the prompt response and listening to feedback.
For underskirt, in the previous version of the game before the covering was added it looked fine to me. I never noticed anything particularly jank or glitchy, at least during those few times I'd be behind her when she was walking up the stairs. Either way, I'd rather have a glitchy ass than the void personally.
Shame about the sandbox mode. I'm not a programmer so I have no idea how much work it'd be and assumed it wouldn't be too much, since it'd just be letting the player modify existing systems, but if it's a big ordeal then makes sense you wouldn't want to add it to the workload. Still, I do hope you at least keep it as an idea, since I think for a lot of people it'd nearly double the value of the game.