If I understand Atlas' new stance on .pdfs, it's your intention to keep four books print only at any given time. What I'm asking then is, will any effort be taken to coordinate the .pdf releases with debuts of new titles that displace them from the 'print-only' list?
I ask because one of my players asked if RM would be made available soon...
Nope. They release whenever we have time to do them. Reminders via the forums likely would help, though. 
It would be nice to have the books in formats that are better suited to ebook readers. PDF is nice on a computer, but don't work so well on a Kindle or Kobo reader.
Just a pipe dream...
In our experience, the variable-width format of readers like the Kindle is really not condusive to the conversion of RPG sourcebooks, which include things like inserts and art.
Just to follow up on Michelle's comments -- my intent is to get the next PDF online fairly quickly after a new ArM book is released in print, but it's subject to what's in my to-do list (which tends to be very full when there's a new book being released) and other factors like how quickly the folks at e23 get a file posted online. So don't be surprised if it's a few weeks to a month.
On the bright side, Michelle has started doing her eBook/PDF conversions right after she sends the book to press, so they're sitting in a folder on my computer waiting to be uploaded -- so making the actual PDF file is not a roadblock.
As Michelle said, the other e-reader formats are not easy to convert to, due to the level of formatting in our RPG books. We own a kindle and have experimented with it a bit, but it does not seem likely that we will soon do RPG books in that format. This may change over time. It's also possible that we may do some things like book excerpts/samples in formats other than PDF (e.g., a Mobipocket/Kindle-formatted document that you could download to your device directly from the Atlas web page). Then we could choose excerpts with restrained formatting requirements or at least a relatively small amount that would need re-formatting.
Like I said, it's a bit of a dream, but I'm quite aware of the format constraints and difficulties.
Thanks for the info and for the efforts! 
In this vein, any idea when "The Cradle & The Crescent" and "Hermetic Projects" will be available in PDF formats?
We're overdue on releasing The Cradle & The Crescent. One of the duties we're putting in Cam's hands is to manage our digital products portfolio, which involves transferring a set of tasks previously done by Michelle and me (adapting printer files for PDF, exporting the PDF, uploading to eBook vendors, setting up catalog information etc.). Cradle & Crescent is the first product he'll be doing, and Hermetic Projects the second (to go online when we release the print edition of Antagonists).