After this 1000th episode with soo much nostalgia the crew feel so integrated, we are with the SH for soo much time, and even the one like Jinbei and Brook are in the story for a decade, a new character joining now that the SH are close to ending their journey would feel soo random.
I like Yamato, but even she and Momo that seems to be the most likely candidades dont have nothing close in development to what the other SH have. A SH that havent gone through the timeskip and the majority of the adventures, there's no need for this, just bring Vivi back, she feel more like part of the crew than anyone that could join now.