Null can turn his nullification powers on and off at will now so when Kurt teleports him he has them turned off
If you attend the classes weekly you get a bonus to the amount of Love and Trust you gain during dialogue , the attendance bonus is also applied to the side activities like dating , training and studying together where the amount of Love and Trust that you get is also increased
The GPA from my experience becomes available from summer , the version that i was playing was 0.6a , the 4.0 GPA is easy to get as well , just attend the classes regularly and study once in the evening and you will get it fairly quickly , to maintain it just attend the classes regularly which also nets you a good chunk of XP , the achievement will be unlocked at the end of chapter 1 if you are able to maintain that 4.0 GPA
Idk what future effects the popularity ranking will have , mine is at 2 currently , gaining popularity as of now is tied to the barbeque event held on Saturdays , just bring some food that each of girls like , ask them beforehand as to what they want and during the event keep the conversation friendly between everyone and the score increases or decreases accordingly
Winning the leader board in either cognitive or combat nets you points that you can use in the achievement shop to buy perks , skill points , clothes for null , music and phone wallpapers
As for the limited shapeshifting , it's effects haven't been shown as of yet