First, a little background information before going to my point.
In the show, Sam knows that Jon has encountered with two women: Ros and Ygritte (Melisandre might count, but I don’t think Sam knows about it.) When Jon describes both women, he mentions their red hair. That is something Sam knows about both of them and similarities. The other known female redhead in Jon’s life is Sansa. However, the differences in all three women is their status (Ros is a prostitute; Ygritte is a wilding; Sansa is a lady).
Sam also knows about Jon’s background and his desires (to be a Stark, not a bastard). Jon’s status is what bothers and limited him before joining the Nights Watch.
In the eyes of everyone in westeros, from all of the three women, Sansa is the one that Jon can never have a romantic relationship with; not because they are related, but because she is a lady and he is a bastard. Ygritte and Ros are closer to his status than Sansa is.
Jon has known Sansa her entire life, and if they make Jonsa happen (my shipper heart can hope) Jon knows can never be with someone like Sansa (a high born lady) because of status and everyone knows that.
Now, image Sam finally meeting Sansa: a high born lady who Jon has known almost her entire life who has redhead, and knows that Jon likes redheads. One can think she is the reason he likes redheads (I am not saying that to be true, but one can assume to be the case). And Sam, giving a smirk to Jon by thinking this.
The point is, I want someone in the show to shine on the Jonsa ship like they made in season six with Bronn on Brienne and Jaime. And who else can be the best person for this other than Sam Tarly?!?!??!?!
Sam doesn’t know Jon was murdered, resurrected, left the watch, reunited with his sister, gathered an army, killed Ramsay Bolton, retook Winterfell in the Stark name, and is now proclaimed King of the North.