Have been tinkering with something similar: https://galapag.us/ I don't have all that much time to work on it but I think by next year I'm going to go back to spending time working on it instead of general compsci/coding nightly training.
I think this is a key factor. Although I imagined some site-based scores for simplicity (like HN karma) they have the disadvantage of being siloed, so you'd be trading one virtual currency for a pile of competing ones, with all the comflicting imperatives of commercial activity). It's better that it be adjusted per user, and maybe other transactions weighted according to mutual perceptions.
I proposed something similar here a few years back when the site was beset with voting rings but it was deemed too complex - and it was, for a site. What I (selfishly) wanted was a filter that would float stories to the top based on whether they were voted up by people I respect. So if my friends Alice and Bob voted a story up, I'd see it prioritized, but something promoted by Carol and Dave would be discounted.