Why tie it to only HN and/or reddit? It could be a choice for users to make, about which sites to correlate with which review sites.
In any case, interesting idea, thanks for sharing!
And for those mentioning gaming, HN does pretty well against all but the most sophisticated and motivated. Browse with 'show dead' on you can see there are plenty of attempts. A link to their profiles on HN and reddit would allow for review of their comment histories in order to determine authenticity/ how closely tastes align.
Even Amazon could allow us to filter reviewers by review history, or other such criteria.
Edit: You are probably right about allowing other identity providers, but the idea was to minimize the addressable market in order to study the dynamics of such a platform. Your comment definitely made me think of it as a possibly viable idea, thanks!
I am surprised there is not a Bitcoin-inspired "solution" to the problem of fake reviews.