Ken,
Thanks. If I am to interpret your response correctly, we are not mapping stationary land units that are subject to climate change (>30 or 100 years), but rather fluid systems that move along the landscape with climate change. The implication is that ecological sites and soil series may themselves come in and out of existence as environmental parameters change. I guess this would be the same as with vegetation associations, some of which have come and gone long ago without modern analogs due to species that no longer overlap in range (as evident in pollen records after the last ice age).
For soils, it means reclassification based on observable properties. But for ecosites, we have the added complication of establishing reference condition based on history. It is inevitable that presettlement condition for a piece of land can no longer be reference condition if recent trends in climate result in cumulative response in vegetation. We need to reevaluate the criteria for determining the reference state.