Quentin would regard Katie with the same cold familiarity her reserves for all former IS members. As a general rule, he always has someone to take the fall for him if he's caught... though that could be an interesting plot for later on.
I think Mei and Demz could definitely be close! Demz likes Mo (but thinks that the Tornados are CHEATERS).
I like the idea of friendships for Sean with Kaitie and Spencer. Sean is bi and really needs some queer friends to hang out with. He (very secretly) had hopes that Leah could eventually be his lesbian partner in crime, but then she had to be all straight. So... friends?