You can, quite trivially, measure the total amount of BTC that moved from wallet to wallet. You can't tell what actually moved from entity to entity (at least,

You can, quite trivially, measure the total amount of BTC that moved from wallet to wallet. You can't tell what actually moved from entity to entity (at least, not without a lot of work, and probably not without some non-blockchain information). I'm not sure how good the former would serve as a proxy for the latter in your envisioned use case. Really, if we wanted to stabilize a coin, I think we'd want to be measuring how it's moving relative to other things, which is definitely external info. It would be a challenge to come up with a means of folding these observations into the system in a secure (and ideally trustless) way.