The Web of Trust (WoT) concept provides for marginal security benefits
and then only in a very narrow set of circumstances that are unlikely to
hold true for the larger community of Tor node operators.
Starting with the second point, the WoT concept presumes that trust
between its members precedes the codification of that trust into
attestations attached to digital certificates.
In other words, the WoT might provide (but likely will not) security
benefits to a group of users that have pre-existing social relations and
trust. For example, members of a human rights group that have personally
known each other, or at least the bulk of each other, for years.