If you subscribe and get ESO+, you get ‘…Access to all DLC game packs available in the Crown Store for the duration of membership’. That does not include the latest chapter; right now that’s Necrom. There’s a new one each year, so you’ll be able to play Necrom next year with a membership if you don’t want to buy it outright.
They do a good job of making the membership very appealing, I have to say. Increased bank space, double the slots for furnishings in your houses, and a bottomless crafting bag, for ex. But they are not obnoxious about it like, say, Neverwinter Nights is.