More hints that Yamato will indeed join the crew... And we have yet to see her "life/motivation" flashback and her permanent "role" (though I think she'll be their scribe/chronicler)...
Yamato having read Oden's journal a drawback? Robin also knows a lot at this point as well, she reads the poneglyphs without us knowing what they are until brought up... If there's something about the Roger Pirates' discoveries written there, then that only proves that Rayleigh's suspicions that they might've interpreted the "forbidden knowledge" the wrong way or that got some inconsistencies or missed major details since they're not scholars, is highly possible... I mean, how would we know Roger Pirates' interpretation once they reach Laugh Tale? If Robin is that "dirty" to get spoilers, she should've accepted Rayleigh's offer to tell the background of the Void Century and the D Clan... Other than Robin, none of the crew is interested about it, not even Nami, Sanji, Franky (who even incinerated the Pluton blueprint), Brook or Jinbe... And yes, Franky also read the Pluton blueprint as well...