To remain consistent with the previous films, the Skullls should relate to some kind of power or energy (life) source which could be perverted into a weapon in the wrong hands, likely on a large scale. In 1957 terms, the Russians represent THE threat to global peace and freedom -- think Nazis on an intercontinental scale.
While Spielberg's films often deal with issues of communication, I don't see how telepathy or holographic projection or alien contact can translate directly into a lethal weapon of domination which Indy must prevent the Russkies from obtaining.