I do not think, however, that this power will be broken. Brook isn’t going to be in a fight and suddenly summon the deceased soul of Whitebeard to fight on his behalf. I would imagine, to fit the themes of One Piece, he would only be able to summon souls that he had bonded with on a spiritual level. Brook could use his power to summon deceased Nakama to assist him.
I think, instead, that his biggest flex of power with the Yomi Yomi no Mi is going to be him summoning the Rumbar Pirates, including Yorki, to assist him in whatever his ultimate fight in the series is.
Imagine this: Brook versus Doc Q and Stronger on Laugh Tale.
Doc Q is a horrific monster. Brook is on the ropes. He feels he’s going to meet his end when, suddenly, a hand reaches out to pull him up. The soul of Captain Yorki helps Brook to his feet and, joined by the rest of the Rumbar Pirates, Brook is able to defeat the member of the Blackbeard Pirates.
This would also make possible for the whole crew to meet Laboon again.
We could get the following scenario: Brook and the Rumbar Pirates’ souls all sing Binks’ Sake along with Laboon’s wailing, everyone crying tears of joy.
*Theory by Feraligreater328