A point in favor of this would be the verbiage - it seems too eloquent for Shirahoshi imo. I remember her as being pretty childish in her expressions
Yeah, the only way I can see it being Shirahoshi, is if she's intentionally trying to convince Loki it's not her... which doesn't really make sense. The Den Den Mushi connection range is an issue, too: I believe the Marines are only able to communicate long distances by sending calls from one Den Den Mushi to another, due to their limited ranges.
Shirahoshi is a "can't lie for shit" character in One Piece, and I don't know why she would lie to Luffy about not having friends in the first place. Like... that would be really sad, honestly.
Shirahoshi is incredibly polite/sometimes childish in her speech (especially when she's excited).
I could see Mosa being Shiki if Shiki grew a beard, and Shiki was trying to trick Loki, but, honestly, Loki is probably too smart for that.
Jarul looking after Harald's son after he died, who everyone else hates, fits his wizened, kindly grandpa character.