Question: If Sion was under Exar Kun during his rule, then wouldn't he know in weaknesses to his old Master's armies? And possibly the weaknesses og Kun himself?
And let's not forget Traya's assassins. They grow in strength (apparently) to match the strength of their opponent. A few of them could potencially assassinate Kun.
I think I might actually be pulling for Traya in this one... Traya vs. G0-T0 Kaggath would be awesome!