We reported last year that this would be happening. At the time we were told it would roll out for New York Comic Con. But I understand that there were additional concerns from certain publishers and the whole thing was delayed while they were worked out.
You can see from this who worked them out.
ComiXology Unlimited is the name, an all-you-can-eat digital comic book service for $5.99 a month featuring thousands of comics from Image, Dark Horse, IDW, Boom, Oni, Dynamite, Kodansha, Archie, Valiant, Fantagraphics, Humanoids, Action Lab, Zenescope and more. Those available in the scheme will get a little Unlimited badge when they appear on the regular ComiXology store.
Currently only available in the US, there’s a 30 day trial starting now.