User blog comment:Kaido King of the Beasts/Chapter 912: A Futile Feudal Life/@comment-80.112.150.83-20180720154343/@comment-7614831-20180722063217

If Zoro were to replace any of his swords with Nidai it would be Sandai, bringing all of his swords up to the O Wazamono Grade; a skirmish against Hawkins' weird devil fruit powers might bring that about, but we'll see.

I think it more likely that Nidai's presence, alongside Sandai, is a precursor to the Shodai Kitetsu turning up in this arc: the prospect of Zoro wielding all three Kitetsu at once is a fun scenario to imagine, if a little unreasonable to expect ^_^