I have a lot of questions in my inbox right now about what purpose I think Cas/Hannah will serve, and I think the gifs above speak for themselves. Seasons 8 and 9 put Cas in a position of being forced to choose between humanity (Dean lbr) and Heaven, but he still finds himself being torn between his loyalties to both. While I would rather things stay platonic between Cas and Hannah, this serves a vital purpose to reinforcing Cas’ choice for his endgame, especially if we’re talking textual romantic deancas.
I do think the romantic vibes between Cas and Hannah will probably be heavy subtext at most, but juxtaposing the two relationships with one another is going to be very interesting. I wouldn’t be surprised if in the top gif Hannah is asking Cas to stay with her instead of going off to help Dean, and Cas will choose Dean above Hannah, above Heaven, above the angels…as he always has, and as he always will.
I think it’s also significant that Hannah goes from singular to plural (I -> Heaven), while Dean goes from plural to singular (We/family -> I). It just highlights the fact that while Hannah may have romantic feelings for Cas, we’re still supposed to view her pleading as part of a ‘cause’. Dean’s, on the other hand, goes from the idea of family, which is already something different from a cause, to completely singular and personal, and thus wholly connected to the emotional relationship that Dean and Cas have.