According to Do I need a Turkey transit visa for a layover?, one doesn't need a transit visa for Turkey if one isn't leaving the airside area of the airport.
Say that a citizen of a country that requires a visa to visit Turkey has a flight booked that arrives on the last day of operations at Ataturk Airport, and their connection thus leaves from the new Istanbul Airport. (This is a likely scenario, since Turkish Airlines' booking system conflates the two airports.)
Will a citizen of such a country require a transit visa for Turkey? Also, will checked baggage be transferred to the new airport, or will one have to claim it at Ataturk and transport it themselves to the new airport and recheck it?