The short answer is that nobody knows.
The long answer is that, if they've done a good job of job balance, we'll see DRK/WAR, DRK/PLD and PLD/WAR based off of personal preference. Or the composition of the rest of the party depending on what kind of utility the DRK has. Like DRK gets int-down and Monks aren't quite as important or they add magic vulnerability so smn/blm become more desirable when you have a DRK.
Many interesting things may happen and everything now is pure speculation until we see the DRK's abilities.

I'd bet on it being decently balanced for any of the 3 combos. The idea that Paladin is default MT over the WAR is pretty much only the product of momentum at this point. Any competent group could use either one MT/OT and I expect that will continue with DRK.

A month before Alexander hard is certainly plenty of time to level a DRK and figure out how it works.