I personally think changing the bodies is a very bad idea. I for one, along many others, prefer my male MC to be androgynous and cute like he is with the current body. But mostly the game is basically about being a vulnerable young girl/boy being preyed on by the people around them. The loli/shota look the characters have right now work a lot better with that premise than the thicc girl/muscular boy would. It would make being a target for every pervert in town look kinda dumb and would only work if you turned the tables around and the MC became the one to do the hunting instead of being hunted. But then that would be a completly different game entierly, and I think it would be better for the game if Vrelnir's time and effort were invested in improving and expanding the core game rather than trying to catter to people who want it to be a different game.
I find half of your second suggestion to be a much better idea. With the penis size for NPC having been recently added, the MC vagina and anus becoming looser with use could realisticly come in the future and could be neat depending on how it's implemented. But I don't think it would be as much of a good idea to have the same system for the penis. Firstly whereas it's somehow realistic for vaginas and assholes to be molded by repeated use, unless I didn't pay enough attention during biology class, I don't think penises grow larger and larger the more you have sex. Even if the game has some more unreal elements like tentacles and stuff, expending dicks through regular sex would just feel kinda silly and it would also go back to what I talked about earlier about the body type. It would make having sex make you grow more masculine and give you a more powerfull look when it should instead be a threat looming over you.
For your last idea I have nothing to add, I agree with you on that one
In any case Vrelnir hasn't disapointed me yet in all of the time I have been following this game, so I trust him to make the right decisions.