Can the Xxcha predict a special victory for Sol or Hakan?
From the rulebook on page 14 (emphasis in rulebook):

Xxcha victory
At the start of the game, the Xxcha player predicts a player and a game round. He records this prediction by choosing a race prediction token and a round prediction token. He places the chosen tokens facedown next to his race sheet and returns all unchosen prediction tokens to the game box (without revealing them).
If the chosen player wins (alone or as an ally, even as the Xxcha’s ally) with any victory condition during the predicted game round, the Xxcha player wins the game instead.

Both the Sol and Hacan Special Victories count as a victory condition. The Xxcha player could predict a Hacan win on turn 8, and whether they Hacan win by stongholds or they win because no one else has, the Xxcha could snatch victory away. This seems like a doable strategy, as long as alliances aren't working to get the game done as fast as possible.