Hi. I've done some more research.
It turns out that being able to create an ESP partition on a bios disk label is a lot more useful than I thought it is. In the cloud space (and when I'm creating an image to be burned onto real hardware) I tend to resize the partition table and filesystems to fit the disk. For a bios disk label that's easy. You just resize the partition and the filesystem. For GPT, there's this thing that you need to move to the end of the disk. You can get the parted command line to do that, but I have not yet figured out to get libparted to do that. So, if you aren't going to have bigger than 2T disks, bios disk labels are a lot easier to work with even for UEFI boot than GPT. If you are using UEFI and bios disk labels, you do need to be able to set the esp flag.
