Update: Adobe has backed down.
When Adobe announced their new DRM a couple weeks ago some said that we would soon see compatibility issues with older devices and apps as Adobe forced everyone to upgrade.
At that time I didn't think Adobe would make the mistake of cutting off so many existing readers, but now it seems that I could not have been more wrong on the issue.
The following video (found via The SF Reader) confirms that Adobe is planning to require that everyone (ebookstores, app and device makers) to upgrade to the new DRM by July 2014.
The video is a recording of a webinar hosted by Datalogics and Adobe, and it covers in detail aspects of how and when the new DRM will be implemented (as well as a lot of other data). If the embed link doesn't work for you, here's a link to the video on Youtube.
The tl;dr version is that Adobe is going to start pushing for ebook vendors to provide support for the new DRM in March, and when July rolls Adobe is going to force the ebook vendors to stop supporting the older DRM. (Hadrien Gardeur, Paul Durrant, and Martyn Daniels concur on this interpretation.)
Update: Adobe has backed down and removed the July deadline.
This means that any app or device which still uses the older Adobe DRM will be cut off. Luckily for many users, that penalty probably will not affect readers who use Kobo or Google reading apps or devices; to the best of my knowledge neither uses the Adobe DRM internally. And of course Kindle and Apple customers won't even notice, thanks to those companies' wise decision to use their own DRM.
But everyone else just got screwed.
If you're using Adobe DE 2.1, come July you won't be able to read any newly downloaded DRMed ebooks until after you upgrade to Adobe DE 3.0. If you're using a preferred 3rd-party reading app, you won't be able to download any new DRMed ebooks until after the app developer releases an update.
And if you're using an existing ebook reader, you'd better plan on only reading DRM-free ebooks until further notice.
One thing Adobe seems to have missed is that there are tens of millions of ebook readers on the market that support the older DRM but will probably never be upgraded to the new DRM. Sony and Pocketbook, for example, have released a number of models over the past 5 or so years, most of which have since been discontinued.
Do you really think they're going to invest in updating a discontinued (but otherwise perfectly functional) device?
I don't, and that's just the tip of the iceberg. Not only will millions of existing readers be cut off, there are also hundreds of thousands of ebook readers sitting on store shelves which, as of July, will no longer support Adobe DRM.
And do you know what's even better? All signs point to the ebook reader market having peaked in 2011 or 2012 (I have industry sources which have said this) so the existing and soon to be incompatible ereaders will probably outnumber the compatible models for the indefinite future (years if not decades).
If you look hard enough you can still buy many of the ebook readers released in 2010, 2011, and 2012 as new, and you can also find them as refurbs or used. They work just fine today (albeit a little slowly by today's standards) but when July rolls around they will be little more than junk.
And that includes ebook readers owned by libraries and other cost conscious institutions.
If you're beginning to grasp just how bad this move could be, wait a second because I'm not done.
Not only will readers be affected, but so will indie ebookstores. They're going to have to pay to upgrade their servers and their reading apps. That cost is going to hit them in the pocketbook (potentially driving some out of business), and that's not all.
Many if not most of the indie ebookstores are dependent on the various Adobe DRM compatible ebook readers on the market. They cannot afford to develop their own hardware so they rely on readers buying and using devices made by other companies including, Pocketbook, Sony, Gajah (a major OEM), and others.
Once those existing ebook readers are abandoned by Adobe the indie ebookstores will probably lose customers to one or another of the major ebook vendors.
In other words Adobe just gave Amazon a belated Christmas present. After all, everyone might hate Amazon but we also know we can trust them to not break their DRM.
Folks, the above scenario spells out all the reasons why I didn't expect Adobe to completely abandon support for the older DRM. It is so obviously a bad idea that I thought they would avoid it.
With that in mind, I would also like to add an addendum and apply Tyrion's Razor. Perhaps Adobe has internal data which says that this won't be a serious issue. I seriously doubt it, but it's possible.
P.S. But if this turns out to be the utter disaster I am expecting, I would like to take this opportunity to thank Adobe for on yet another occasion giving DRM a bad name.