If Unit A is targeted by Void Seeker, and Tideturner flips to swap places with Unit A, does Tideturner become the new target of Void Seeker?

Ruling: No, Tideturner does not become the new target. Once a spell or ability chooses a target it cannot re-choose targets, and swapping positions does not swap targets.

Nuances:

• Depending on the targeting restrictions of the spell, the original target may or may not be legal after the swap (if it's not legal anymore the spell resolves to no effect)
• In the case of Void Seeker specifically, it still resolves normally since Tideturner must be at some other battlefield location and it swaps with Unit A