Recently, I've started reading CITY, the manga that Arawi Keiichi started working on after finishing Nichijou.
There are apparently some Nichijou cameos in CITY, such as this blue-haired mangaka named "Naganohara Daisuke" who briefly appears in chapter 25, and also this book cover by someone named "Ogi Wataru", which briefly appears in chapter 59.
Does this mean CITY and Nichijou are set in the same universe? Or are these just easter eggs? Is there any other evidence, for example, word from the mangaka, or perhaps any additional cameos?