In order to produce a native 4K image in 3D you need two projectors, otherwise, the 4K resolution is split in half when it turns into a 3D image.
In response, Billy Lynn’s Long Halftime Walk is being produced in a number of different combinations, in order to show the film off in its best light under different circumstances.
The major stumbling block appears to be the pair of Christie Mirage 4K laser projectors which have yet to actually be installed in any movie theaters so far.
How many theaters would be upgrading to these new projectors is unclear if they were actually available, but it appears the option isn’t even really there yet.