This requires a newer mkimg.
We should also not enforce 128 as the minimum number of partitions, but that's quite a bit harder to do correctly.
It's a lot easier to not do the 512e/4kn optimization, which will fix gpart restore (and gpart recover) for newer mkimg images.
We should do the optimization when making a brand-new partition scheme / partition. However, we shouldn't when restoring / fixing an existing drive, since the data is at fixed offsets that we can't really affect. We already allow it on read, and this just extends that to scenarios where we're effectively dealing with extant partitions.