Yaaaaaas, preach!
Though while I love Katakuri as a character, his story is a bit too historically intertwined with the Big Mom Pirates for him to be a genuine Straw Hat (would consequently be more suited to a general allied role methinks).
Yamato on the other hand seems to make a lot of sense, particularly after this chapter's revelations...
• We have learned that she idolizes Oden, so maybe she will want to retrace his footsteps by sailing with the prospective Pirate King?
• There's already a sense of budding camaraderie between her and Luffy?
• Also seems kinda baka?
• The Ace factor?
• Maybe Oden's logbook contain specifics about the poneglyphs and she can guide the crew with Robin and Nami?
• The Zoan factor, if there is one?
• More of a pet peeve of mine: the Straw Hats have exactly 0 female brawlers/heavy-weights (Robin is a middling fighter in the New World), so she would fill a void?
• No strong allegiance to the Beast Pirates, in contrast with Katakuri-BMP, so she could become a dyed-in-the-wool nakama?
At least in terms of eliminating factors, the only major reasons for her not joining might be: she wants be become Momo'/Hiyori's retainer and reckons it's her duty to serve Wano (like Vivi in Alabasta), or she knows way too much about Laugh Tale because of Oden's logbook and doesn't want to play spoilsport in the ultimate adventure.
In fact, given her pedigree as the
Strongest Creature's daughter, I'd be perfectly happy with no further combat-heavy additions as the Straw Hats would fare quite well vs. the Roger Pirates in mano a mano comparisons with her addition (narrative-wise and with regard to projected fortitude):
Luffy ~ Roger
Zoro ~ Rayleigh
Sanji ~ Gabban
Yamato ~ Oden
Jinbe + Robin ~ Inuarashi + Nekomamushi
The only remaining piece of the jigsaw, in my headcanon, would be a future yonko-tier apprentice, like cabin boy Shanks with Roger Pirates or Kaido with Rocks Pirates. Be poetic if it happens in Elbaf as that is rumored to be Shanks' arc!