I have not investigated the issue of techeiles enough to even begin to have a thought on the matter, but I want to just call attention to what I think is an interesting methodological point R’ Asher Weiss makes in discussing the topic. From the response, it appears that the person writing to R’ Weiss made the argument that the vast numbers of purpura/murex shells found in Eretz Yisrael proves that this species was used to make techeiles. Rav Weiss responds that he recognizes that this type of argument/evidence carries weight in various fields, particularly archeology, where the goal is to construct a theory that best explains the available facts. However, a theory, no matter how plausible, is not proof. Whatever explanation is offered for the evidence remains just one of many possible explanations, some more likely than others, but none of which can be said with certainty to be true. Halacha demands proof – not just a logical or plausible theory.
Sorry if this cut and paste of an image of the relevant part is a bit sloppy: