That's why the discovery of the mythical "any idiot artifact" is so much more important in the public relations sense than it is in the academic/scientific sense. Moreover, you have to contend with the fact that people generally love a mystery more than they love the solution, especially a mystery that's as deeply ingrained in the consciousness of a culture as this one is.
Yes; academic opinion and public opinion may not necessarily reach the same conclusion at the same time. I tend to believe the mystery will be solved by an accumulation of evidence that is consistent with the Niku hypothesis (as adjusted over time), which will eventually reach a tipping point where it seems that a landing on Niku was the most likely outcome of the various possibilities. But, of course, if an "any idiot" artifact is identified, that would be great.
However, even if such an artifact were discovered, the point about people loving a mystery is well taken. People will always be able to come up with alternate ideas, even to explain the presence of an "any idiot" artifact (e.g., it must have washed up from somewhere else ...)
As for (hypothetical) bones in Fiji: a lot would depend on the circumstances under which they were discovered, and what was known about their provenance. Who had them, where that person got them, what container they were in and where that container come from, what labels or addresses or directions or identifying marks accompanied them, etc.
I also wish Lambrecht had been much more specific!