Create a section for rumors where users can vote the likeliness
Post unconfirmed speculation in its own separate, database-like section. Allow site visitors to vote on the likelihood of rumors and routinely test the predictive capacity of the site's audience. This way, encourage the tracking/posting of more rumors (which can be fun and entertaining) without front-paging too many articles with "grain of salt" caveats.
Alec Kubas-Meyer commented
The only question here is whether or not we have enough of a community to do that. Dtoid could definitely pull it off, but we only have a dozen or so non-editors who consistently comment on things. I think this is a really interesting idea (especially if there was some sort of prize if people got things right), but I expect we need to be a bit bigger first.