0/ Thanks to @coinmetrics for rolling out their "Realized Cap" data. While definitely an imperfect measure it can also be used as a decent approximation of average cost basis of current holders. Let's look at $BTC below: 
1/ At present the $BTC market cap is ~30.0% below the realized cap which is a bottom 0.3% of observed periods going back to 2013. The only periods of greater divergence was during January of 2015.
2/ This really doesn't have any predictive power for forward returns given the one off nature & cluster of 7 consecutive days; but shown attached.
3/ What's even more powerful is charting this as a % difference. Looked to call the top in both '13 and '17/'18. Has also been good at near term bottoms.
4/ If we look at the difference between realized cap vs. mkt cap for $BTC over time it's actually been a pretty good indicator of local tops & bottoms over extended periods of time. While the rate of change is applicable on even shorter time frames.
5/ Another big thank you to @coinmetrics & @nic__carter for providing pre '13 data to look at this on a longer time frame. A snapshot of the difference between "mkt cap vs. realized cap" theoretical cost basis over time & $BTC monthly returns:
