This appears to be another question in which we need to know of someone currently has one of those monitors and is playing Civ V to find out what the answer currently is to Civ V, which most likely will be the answer for CD release of BE. (All the news about 4K monitors I see is from 3 days ago, they might already be manufacturing the CDs even with this being a steamapp.)
Now if it doesn't fully support the resolution when you buy it and if its also simple to add, an early patch post release might add it. (Who knows, might even make day zero patch if someone asks Firaxis nicely about it)