In general, the theory is interesting
And I have an important question, which ancient weapon were Roger and Shiki talking about?
Roger was unable to read Poneglyph so our only guess is Uranus..Did Franky's teacher give information to Roger, and then the question is, how did Shiki know that Roger knew?
I usually don't introduce logic into the story, but I think these questions are important if Oda doesn't want to introduce contradictions into the story