Well I am a subscriber and bought the game when ZOS made an offer with many DLCs and zones so yesterday I checked wich areas I can visit thanks to my subscription and I found out it was just the clockwork city, I got murkmire free from the daily rewards and IC I already owned but i count murkmire still as a benefit because I did not pay for it.
I am not very interested in DLCs that are dungeons because most of the time I do not want anything from those dungeons and they just reward me with one skill point but exploring and seeing new "worlds" with stories I love that.
I don't know if there is more people like me that have eso plus and would like more DLCs that are a zone added.
I am rather new I bought the game 1 year ago but just did the daily rewards and started playing just a few months ago so I do not know how the development circle works but maybe they added an expansion, then dungeons and maybe they will add a DLC zone next, if that the case I would be super happy with my subscription.