It seems like a strawberry pie would be good. Maybe the flavors compliment each other like you said. Often times it seems like tart fruit is mixed with sweet fruit in pies and things. Blackberry jam tastes better with a bit of lemon in it I've found, (plus it thickens better).
Could it be that the rhubarb helps thicken up the pie filling?
I tried to google the answer and I think it's the sweet and sour combo that makes it work or at least that is the only information that I could find. In any case, I would still like to find a strawberry pie around here. They have blue berry and raspberry, might as well have strawberry too.