At this point, there haven't been any indications that Disney is planning on repeating the 24-hour Leap Day event from 2012. There are no unusual blockouts on Feb 29, 2016. They have done 24-hour days on the Friday of Memorial Day weekend in 2013, 2014, and 2015. So it seems more likely that they'll have one then in 2016 (based on the blockouts).
I've been the 24-hour days in 2014 and 2015 and they were markedly different events. The one in 2014 was pretty calm. There was a bit of a crowd at opening and again in the evening when folks got off of work), but other than that, the crowds were quite manageable. Probably less than a peak summer crowd (it was quieter than a mid-July crowd).
The one in 2015 was an entirely different experience. That one was very busy. It was the kick-off to the 60th Anniversary Celebration, so DLR debuted the new fireworks, parade and WoC that evening. DL reached capacity in the mid-afternoon, although that was mostly due (I think) to the crowds waiting for the parade and fireworks. The attraction lines were long (like peak summer). Food lines were super long (worse than summer).
I have trip reports written up; see the links in my Signature.
