This is actually kind of huge, because this isn’t being reported as “sources say,” it’s the “Clinton campaign” on the record saying Elizabeth Warren is “under consideration to be Hillary’s running mate. BUT… listen to how it was reported:
My reporter’s Spidey-sense tingles whenever I hear on-the-record reporting without direct quotes, because it sounds to me like this is being massaged a little bit. If I had to guess, I’d say that the campaign’s emphasis was probably on shooting down speculation about the meeting, and the campaign probably said something along the lines of Warren is one of many who are under consideration, but they haven’t started interviewing anybody yet.
In any case, narrowly reporting this as “Warren under consideration” creates an expectation that’s really not great for Hillary no matter how you slice it. Voters who might have preferred a more centrist pick won’t have time to get used to Warren if she is, indeed, the pick, and those who are pro-Warren will now be that much more disappointed if she is not.