The Beta EASyBCD version works on a GPT VHDx, it booted.
Hyper-V results :
Gen 1 - Treats VHDx as IDE file, result "Boot failure" message
Gen 2 - Treats VHDx as SCSI file, "Boot failed, EFI SCSI Device, No operating system was loaded"
Now this might be out of scope for your roadmap or...