I just had a brief look at the script and I'm still unfamiliar with armbian-config tools and the image building process, but I see 3 options for nand-sata-install:
GPT Capability checked against a hardcoded list of platform that supports it. GPT is preferred if available.
An input/option for the script - but as to be validated with 1.
The script replicates the partition table type of the running system
If the sdcard images are now generated with GPT when it is supported, then I think #3 is a good option. What do you think?