New quest in Chapter 10? Huh, weird and interesting... If this is in the February update after this patch, that would be interesting, but not much to base off from, perhaps a playable section in Cartanica?
To be honest, it has to mean we are getting some form of an expansion there, be it story and/or environment. There are only 2 places you go in Chapter 10, the train station and the dungeon. The dungeon is linear, so there is no room for an extra mission there, and the station is...a station lol. It is pretty possible that they may have made Cartanica explorable to some degree. Unless they expanded the dungeon but I just don't see how.
On that note. I got a response on reddit from r/FFXV's mod after he deleted my post for relaying this info on Reddit:
scissorman[
M] 1 point 7 minutes ago
"As they have removed this information, whilst we've actually archived the original page we are choosing to wait until it is publicly released to prevent potential confusion and/or misinformation.
This is purely due to the fact that the 1.21 update information was added early, with an incorrect date and that the JP patch notes for the next one has been not only amended, but removed completely."
It seems that the Japanese website likely uploaded the wrong patchnotes, due to the timing confusion. This is 100% in fact happening, but likely right before the Royal Update DLC hits.