Well, the format is quite different, but I think the new Monster Builder in the adventure tools is a terrifice first step in that direction. I miss the fluff and the art, but what it provides is a database of monsters from all sources, that will be updated regularly.
I don't want to be too much of a raving fanboy here -- I'm sure there are many great threads talking about the strengths of the monster builder. Ultimately, I think this is the direction that they're heading -- a controled, subscription driven way for them to put this content in our hands digitally. It's available offline, so you have that, but it's not going to work on yoru kindle or other ebook reader.
I liked the PDFs. I bought every book in the 4e line in both print and pdf, and I found use for both versions. And I miss the PDFs. But I think if you're expecting that the replacement to PDFs would look like PDFs, I think you're going to be disappointed with whatever they come up with as a digital enhancement to the game.
-rg