As I've stated in the thread above, cloth and mail coifs - commonly worn under a helmet as padding to help disperse the energy of the strike - are locked under the Jewelry category, which limits combinations to some degree. While the issue can be dismissed in the case of full helmets covering the entire head, it becomes jarring when one looks at the open helmets, such as morions, Ottoman style helmets or venerable nasal helmets - or those that have visibly exposed neck. It would open new possibilities for helmet-wearers to be able to pick between an option with the coif already attached to the helmet model, and without.
In the future I will list the ID's of helmets that would benefit from it.