So how about this:
In this episode Satsuki's Kamui is referred to as her
Wedding Dress. We also see in the ending animation a shot of Ryuko
looking at a wedding dress while window shopping.
We also know that another half of Ryuko's scissor blade exists (which she believes to be in Satsuki's possession). This could easily be a reference to the saying
"Marriage resembles a pair of shears, so joined that they cannot be separated, often moving in opposite directions, yet always punishing anyone who comes between them." This could be interpreted to mean the girls, who have opposing temperaments and color schemes, but that may be unrelated to the saying.
The red "Life Fiber" that Ryuko has been absorbing in to her Kamui could also be a reference to the
Red String of Fate. Those connected by the string are destined lovers, regardless of time, place, or circumstances.
I speculate that Stupid Sexy Sensei (who appears to be the last person who knows the true powers or purpose of the Kamui and was actually physically getting ready to break up the fight this episode) isn't undercover to assist Ryuko directly, but rather is undercover to determine if Satsuki and Ryuko are potential brides. He'll be the final boss that they have to team up to defeat.