1. A veritable turnover of the Parties in which Oklahoma takes part. Think of my Obama-Eisenhower overlay map, The political orientation of the States does not change, but the Parties do. Oklahoma went R for Eisenhower and against Ike, but it was reliably D as late as 1948.
2. A huge infusion of Latino voters. This is not happening as swiftly in Oklahoma as in some other states. (Mexican-Americans seem to be moving heavily toward states with good results in public education, and Oklahoma is not one of those states).
3. Complete collapse of the Republican Party, in which case Oklahoma decides nothing.
Neither is likely.
Latinos are actually trending rightwards, and I would bet the kind of Hispanics to live or move into an evangelical conservative state like Oklahoma aren’t exactly likely to be friendly to the Democratic Party.
The Dems best bet is an influx of black voters into a state like Oklahoma (look at what happened to Atlanta/GA) or younger, white liberal millennial suburbanites (again, look at Atlanta, but also look at the Austin areas for a more pure example).