I do plan on content involving Mara being nude or in her underwear, I however never promised a "nude mode" as you put it. Mara will be able to wander naked through gameplay progression.
In regards to other characters being nude, well every other character that is seen at this moment is nude (the two characters that were added this update, and the two that exist in one of the endings, that got names and backstory this update).
Regarding scenes including nudity, all of them currently do. I actually want to add variation to the sex scenes that are more in line with what Mara is wearing, because I like immersion like that, but it is a "towards the end" kind of inclusion.
Overall, if you take some time to play the game (all current content should be viewable in under 30 minutes, if you speed and use things like the wine in the start room that you can spam for lewdness for right now) you will find that currently it has ALOT of nudity.