Dear Peter and Andrew,
the current draft of the DHARMA encoding guide says <space type="hole"> which is also the way I handled copperplate binding holes in the Siddham corpus. I prefer the simpler "hole" to the more cumbersome "binding-hole" but if you, Andrew, have already used "binding-hole" a lot and would prefer this more accurate term, please convince me to adopt it for use in DHARMA. (Fyi, I our guide prescribes <space type="defect"> for all spaces left blank due to physical defects in the surface, so "hole" is not in my opinion ambiguous.)
Best,
Dan