In order for a customer base to know whether or not they are getting value for money a service provider needs to be transparent in what they are offering.
From the rather sparse 'Road Ahead'
ESO PLUS
The easiest way to take advantage of the Crown Store and Tamriel Unlimited is to be an ESO Plus member. As a member, you'll get bonuses to many in-game leveling systems (experience point gain, inspiration gain for crafting, etc.), 1500 crowns to spend in the Crown Store each month, and access to all DLC game packs for the duration of your membership. Existing ESO PC subscribers will automatically be enrolled in ESO Plus when Tamriel Unlimited launches, so no further action will be required to become a member if you're a subscriber at that time.
******
Thing is though - how can we decide about whether or not to subscribe when we don't know how much DLC is planned or how much Crowns cost? Also - the other perk - exp/insp - total junk.
I recommend ZOS you go over to EQ2 and there you can see some decent reasons for subbing per month.
Unless 1500 crowns costs £10 there is no reason to sub currently as there is no DLC being discussed, no real 'Road Ahead' information that we didn't already know and certainly nothing to make people really feel Plus is worthwhile.
Also, on another note - what is to stop someone playing for free, then, when DLC gets released, subbing for a month to play it, then after completing the content, unsubbing again?