I know this came up earlier, and I don't know how much play it got. Anyway, everyone kind of thought it was a pipe dream, but dig this new-ish article: http://www.maizenbrew.com/2013/5/18/4341600/Johns-Hopkins-Big-Ten-lacrosse-conference-realignment.
One potential snag is that they want to keep their ESPNU deal, and also join for a five year trial period, but jumping the hurdle of them actually deciding they want to join a conference is huge (a la Notre Dame), and they have done that. They might seem like a stronger fit with the ACC with their lacrosse focus, but if their intention in joining a conference is finding one they can get to the tournament with, the B1G is the better fit, as it's probably weaker overall, and there is some fit with the new Mid-Atlantic members as well as new Midwestern recruiting grounds. It's looking like this could really happen.
EDIT: From late April: http://www.collegecrosse.com/2013/4/29/4280178/conference-realignment-big-ten-b1g-lacrosse-conference-johns-hopkins-maryland/in/3696323. Apparently Gene Smith said the B1G would bring in an affiliate member for lacrosse. So there.