I would be wary of having any single reputation system, anything can be gamed. However, I'm also wary of making things too complicated (I'm an expert in making things too complex). Plenty of us have IDs on existing systems elsewhere, but without any way of really making use of this, I don't see how pre-existing reputation will help a whole lot.

Once upon a time, I'd have said personal certificates. A class II personal certificate required that you produce two items of proof of ID and be available for a callback, and a class III personal certificate required that the signer actually meet you and that the ID included photo ID. Hands up all three of you who can even remember that far back. Ok, now just those who can remember that far back without the aid of diaries and/or caffeine. Class III certificates may still be in use by the military, but I don't recall seeing them in general use past the first few years SSL existed.

Here's the other problem. Security. A WoT is only good if the spiders are friendly. Just one bit of toxic slime in the mix and phantoms become legends whilst actual legends become worms. The only way to avoid that, as far as I can see, is to have anchor points (not necessarily people) where those anchor points serve the sole purpose of preventing trust by circular reasoning.