I wonder what will be the final trigger to make it official (the yuri). Personally I would love a classic kiss without words after some dumb teasing and Keiko to take the innitiative almost without thinking (and no alchool involved)... But I don't think Shou will be happy with just that.
I would love for Keiko to take the initiative because so far Ran's been the one starting stuff and kinda showing her feelings a little more.
But yes, I don't think it'll be so simple. While I love their playful dynamic, my biggest fear is also that if anything happens (a kiss, confession of feelings, etc), the other person / both of them will play it off as a joke or prank, and cue angst? Not that I mind angst, but I want to see their relationship go forward, rather than backwards.