I found this site, BitNodes.io and thought it might be of interest to some.
In economics, “velocity” is a measure of how many times the same currency gets spent by various persons. As this article in Wikipedia explains, it is not all that cut-and-dry. There are disagreements among economists regarding the determination and the effect of velocity.
With that as background, I found the website Bitnodes.io that is tracking how many Bitcoin nodes are active and from where. They have conducted 10 runs so far. While this measurement is of something somewhat different than what most would consider velocity it does help show something similar I believe. Using BitNodes data over time could help develop a “feel” for the amount of Bitcoins being held (ie. hoarded, saved, lost etc) compared to those actually being spent. If there is a sudden rush of new nodes suddenly becoming active then that could be an indicator of a rise in velocity.