It will probably be on all armor. However, meeting the skill requirement will only give you extra benefit, if you don't meet the requirement the armor will function just like before.
Good point. Looking back, it appears this stat was introduced in the Dec 2015 update. So MA have had this on the cards for a long time (assuming this field is used for the stat)
Armor requirements have not yet been implemented, and as such were not included in the release notes for VU 15.15.0. The requirements and benefits will be included in a future VU.