Not sure how committed I'd call Willow and Tara at this point; this is just hours after they get groiny for the first time - OK, for those two, that IS commitment, but it's several weeks before Willow seriously considers leaving Tara for Oz. Would she leave Tara for Buffy? Though I like your scenario too.

I'm still convinced that Faith totally fingered herself blind in that bathtub after the switch.

Wait, you're saying it's not canon that she did? Let's see, where's the script...

Faith is in the bath. Her head breaks surface suddenly with all attendant splashing, her hair slicked back and pure enjoyment on her face.

She settles, slinging one leg over the side of the tub. Rubs the water out of her eyes, then looks at her hand, flexing it. Feeling the fit.

She looks down at her new body. Runs a hand up her leg, under the water.

She leans back, eyes shut -- then bursts out laughing.

And people say Buffy/Faith never really happened...