LG UltraFine 5K firmware update
After about four weeks I got a reply from LG support with a firmware file attached. 

Here is some information about the file:


Filename:
MODEL_27MD5KA_SV3.04_CV1.13_HV5237_NV3.04_AV0.1e_20170705.zip
Filesize: 304347 bytes
MD5: b03322ad668849ee5112ce24159c5c93


It's an encrypted ZIP file that can be opened with LG Screen Manager. With that file, I've successfully updated my monitor to version (3.04,1.13, 5237,3.04,0.1e).