I wholeheartedly (want to) believe that had niles and CC not been interrupted during their famous couch kiss, they would have had couch sex.

you are right and you should say it

nothing else explains how CC clearly leans into him even more right before the door opens or how they still held onto each other once they realized they had an audience OR how Niles blows her a kiss (!!!!) right before she leaves and how CC shivers (!!!!!!!!)