Recently Comixology announced that they would be adding a subscription service, Comixology Unlimited. This isn't anything absurdly abnormal and subscription services for digital comics are actually fairly common. My Facebook feed is usually cluttered with offers for various manga subscription services and I know that Marvel has already launched their own subscription service, Marvel Unlimited. (On a side note DC and Marvel's comics are not part of this service.)
Part of me is always leery, however, of this sort of thing. You don't really "own" digital comics since the publisher can always yank them whenever they want and copies tend to only restored to buyers (or they're given a refund) once the media catches wind of things. A rental service (since that's essentially what this is) gives us even less control over things. There's also the obvious bit about digital copies not living up to paper, but that's sort of a given.
Still, the idea of being able to try various comics is fairly enticing - especially since comics (digital or paper) are pretty expensive. It's always a bit of a crapshoot when it comes to picking out new things. Sometimes you can rest a little easy if you're familiar with the author, but even that's no guarantee of enjoyment.
I do wish that there was a way to know exactly what comics are available under this service. We're given a list of some of the publishers, but not really any way to verify which ones will be offered as not every digital comic will be available under this service.
It looks like you can tell which ones are offered by checking a little box at the top of the search function and when you search through genres there's a little bar across the book that says "unlimited".
So far the selections aren't really making my heart race since they're just the first 1-2 volumes of various series, some of which are already fairly long running. It's not a terrible way to get into a series, but it will prove to be frustrating for people who cannot afford to purchase digital volumes at $8-10 a pop.