I like this proposal a LOT because it would add a dimension to "trustworthiness" to reputation scores that we just don't have now. As you point out, right now someone can pump 500,000 Steem into the system, engage in dodgy voting and vote buying, and be at 72 in a couple of months... without really having contributed much to the community.
As opposed to someone who earned there 72 as a result of leaving 10,000 engaging comments over a 12-month period. That DOES make a difference! Now, would some (unscrupulous) people find a way to game and abuse this? Probably yes... because some people make full time careers out of "messing with the system."
Great idea, though!
Absolutely @reddragonfly! We need more dimension to better judge just how well one has "earned" their number here. A pure blue should be sought after and celebrated. A warmer tone would give readers a healthier sense of a user's past without having to dig and dig (and scroll) down their feed for context.