Breitbart is barely better than faux news when it comes to credibility. This is the process: find some benign document which may account for some possible kind of change in law, make all the out of the world assumptions you can, make a clickbait article which doesn't say anything worth reading, hope that you typical user doesn't have adblock.

All in all this doesn't mean anything solid. US issued 1 million green cards in 2013, maybe a little more in (FY) 2014. Generally most people these days get them via adjustment of status, which adds the interim benefit of an EAD - so we can add another 800,000 there. DACA adds another ~500,000. Then we have all other categories outside of AOS and DACA. All in all my guess is that it will account to about 3-4 million cards. Now, the order is base of 4 million with possibility of up to 34 million, unlikely it would ever go that high, but going for 4-34 million covers anything in between, like a much more manageable 14 million should reform pass.

So, what they uncovered was a memo which takes into account that reform may pass, but it doesn't assume so. If it did, it would likely ask for a much higher minimum. In 2010 when the Dream Act came close to passing USCIS had already begun drafting regulations the day before the senate vote.
It's not uncommon for an agency to plan for contingencies, let's say it doesn't and reform passes, and then what happens? All hell breaks loose because you have millions of people doing infopasses to get interim stamps/letters, phones don't stop ringing asking what's the hold-up, and considering they have a single printing center in Kentucky suddenly having to deal with 3x the load would backlog them at least a good year.