Please prioritorise this, your competitors are catching up, and once they offer iOS nested/heirachical tagging you will loose a swathe of customers.
This was one of the killer functions that got many customers on board.
I have been a loyal Evernote customer/user for years, and have watched on in frustration as this request has not been addressed. It is commented on in numerous online reviews and podcasts, and YouTube shows, but all changes/updates Evernote makes seem to take EN in other directions that don’t help iOS users that would represent an important group. Frustratingly, I recall this feature once was available years ago in EN iOS, but was removed (but stayed available in android and other platforms), and was available in now defunct third party EN apps (Clever note?) which I tried using in desperation.
I believe Bear notes app already has this function, and many customers are switching, I am investigating that one. OmniFocus has just implemented hierarchical tags, so you will be loosing customers to that app who have been using Evernote as a GTD/task manager, including me.