A long time ago, it became useless to talk about Linux market share. And more recently, it became useless to talk about Linux desktop market share. This is because "desktop" is too broad a term. There are a lot of special-purpose machines out there, and Linux long ago reached parity with Windows for these embedded/kiosk purposes. How many of these are point-of-sale terminals, or handheld scanners in a warehouse? It's impossible to tell.
I think we should change our perspective 180 degrees and, instead of asking "what goes Linux do?" we should ask "what doesn't Linux do?" and go from there.