Okay, I noticed a nod to a previous series, and what might have been some foreshadowing, when I rewatched Ultraman Mebius & The Ultra Brothers .
First, remember the scene with the mayor on the train? The ring tone for his cell phone was the jingle that played during the eyecatch on Ultraman Nexus.
Second, when Zoffy and Taro showed up and restored the energy of the other Ultra Brothers, the Color Timers for Ultraman, Ultraman Jack, and Ultraman Ace didn't turn blue, but became green instead. In other words, that might have been foreshadowing the appearance of their counterparts in Great Decisive Battle! The Super 8 Ultra Brothers. Or maybe I'm overthinking it, and it was just a coincidence.