At this point I think Valve is more likely to be disrupted from an outside influence rather than within, I think a lot of their actions are about keeping the ship steady. If someone does come along as an upstart in a new market as valve did with digital distribution versus retail/physical, the old is unlikely to be instantly irrelevant and obsoleted, and even then you get new markets like mobile appearing over their lifespan where both are healthy side-by-side.