Catsi's thought of the day.
In chapter 311 we see Sai studying about relationships, in it he reads about suffixes and states that in order to grow closer one should stop using suffixes.
Sakura has never ever used a suffix with Naruto this is doen deliberately throughout the manga at first to show dislike of him, and later to show her closeness to him. this is done with literally no transition as we see Naruto grow closer to Sakuras heart
from an Anime FAQ
QUOTE
no honorific -- The lack of the use of an honorific either indicates rudeness or disrespect on the part of the addresser, or it indicates that the addresser feels a sense of intimacy to the addressee. The degree of intimacy is reflected on whether the addresser uses the addressee's family name or given name. Ryoko addresses no one with an honorific, portraying the rude gaijin (foreigner). Because Tenchi uses no honorific to address Ryoko, it gives them a greater air of intimacy, even if Tenchi favors no one girl over another (per 101 Secrets).
Naruto always addresses Sakura as Sakura-chan this hasnt changed ((YET)) from the beginning.
from the same faq
QUOTE
This is one of the more intimate honorifics in Japanese society as it has a more feminine take. It is primarily used for young children, girls, and pets. Girls will often address each other with the -chan honorific
Now if we take into account Narutos now broken image of team 7 and Sakura as pre shippuden team 7. then it very well may be that he has called her that both as an affectionate name as seen in the definition below
QUOTE
Chan (ちゃん?) ("kins") is a diminutive suffix; it expresses that the speaker finds a person endearing. Thus, using chan with a superior's name would be condescending and rude. In general, chan is used for babies, young children, and teenage girls. It may also be used towards cute animals, lovers, close friends, or any youthlike woman.
then we come to uynderstand a little better Narutos perceptions of Sakura.
What I find interesting is this. I have a feeling unconfirmed i grant you that we may soon hear Naruto address Sakura with out the ever present chan suffix.
this may be the first big step between them in their relationship as it moves forwards.
for Naruto it will represent that dropping of the thought of Sakura as the same little girl who always chased Sakura and his acknowledgemnt of her growth as a woman.
for Sakura it will be a bit of a suprise as shes used to that suffix being there.
it will be very interesitng to see where the two go from that point.