The Linux world can be a crazy place sometimes. One minute, Distro A is on top of the world, the next minute Distro B comes out of nowhere to dominate the landscape. I think the biggest market share gains (from distributions that exist at the close of 2015) will be from elementary OS, openSUSE, and Fedora. What sort of gains are we talking about? I have no clue. But, mark my words, it will be noteworthy.