Becoming the WSS is not a competition with others really. As longs as Zoro becomes strong enough to beat Mihawk, he's good.
If Zoro vs King was something to help Zoro learn the Fire cutting technique, I would be more favorable for it, but, as of right now, I don't see Zoro fighting any Calamity.
He said Ashura was his last attack. It's not something another character said, it's not a SBS, it's not some weird interpretation. It's something the character himself stated. The character himself stated he was at his limit.
Marco's healing ability does not, as far as we know, heals fatigue. Even if he fix all of Zoro's broken bones, he should still be needing rest for a while. During this time, it's the time the Calamities should be dealt with.
After that, I'm all for Zoro getting back up and fighting against one of the Yonkos again. Getting instant heal after all the mentions of how severe his state is, just to fight an opponent that currently brings nothing to the table for him, is not something I can support.
If King shows something special that justifies his fight with Zoro, I'm open minded about it, but it's not the case currently.
Btw, about Kaku. 2 things:
1- In giraffe mode, Kaku wasn't even using his swords anymore. Dude was using more his nose.
2- Zoro vs Kaku had a plot closure with Paullie asking Zoro to tell either Kaku or Lucci that they were fired. Sanji had nothing to do with this plot, since during the events at Galley-La, Sanji was roaming Water7 following Robin. He had no interactions with the Galley-La plot.
King has nothing like it.