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What mess? Unity is getting to be quite tolerable. Gnome is forging ahead with their vision and Mint provides a nice alternative to Ubuntu with several different UIs. I don't understand the argument that this is "bad". People have been saying that since the dawn of Linux and it's boring and an non-point.
If you accept that "PC" has peaked, Valve/Steam is screwed anyway. If consumers keep flocking to iOS/Windows8, let alone to Android... then Steam will die a painful death and modern computing will be reduced to mindless one-at-a-time "apps".
Ironically, the "mess" of Linux desktop is the only platform that isn't going for a signed, verified, OEM only software model eroding consumers' rights and freedoms along the way.