If the chart is accurate, then the avg return for the next 10 years will be ~6%/yr. Is that better than other asset classes assumed returns? Given the state of real estate, bonds, commodities, etc....I'd say yes. I don't see this chart as a reason to "run for the hills" now but if we get back up to historical highs then its time to re-assess and go more to cash.
I tend to look at stocks on a bottoms up basis, so this chart, while interesting on a macro basis, doesn't really help much there. Just gives me an indication of whether the investing climate is in a tail wind or head wind mode. Looks to be in the "slight" head-wind category to me now.