I haven't read the books either but watch Prince Oberyn's body language closely when Tyrion demands a trial by combat.
He sits up... very intrigued & highly anxious.
(As if to say... "Little man got some MAJOR BALLS. Go figure.")
Out of everyone... I think Oberyn's reaction had the most foreshadowing.
Then I watched the preview for the next episode 7.
We see someone we haven't for a REAL LONG TIME.
THE MOUNTAIN.
I think Tywin (and/or Cersei) will demand THE MOUNTAIN fight Tyrion.
He sees it as his last chance to kill Tyrion... like he's always wanted to since his birth... and will feel justified in his choice.
Now if he does.... then Prince Oberyn will fight for Tyrion.
AND THIS is the climatic battle that has been brewing all season long.
It makes sense. (to me)
Oberyn has wanted to kill the Mountain since he first got to King's Landing.
And that shit will be on some TROY shit.
Prince Oberyn gonna go all 'Brad Pitt' on Boagrius... I mean The Mountain.
Wait for it.