Warning: contains spoilers for Future State: Superman of Metropolis #2
It's obvious by now that Superboy is a deeply flawed hero and, frankly, in way over his head. Heck, his first attempt to save Metropolis as the Future State's Superman involved him shrinking and bottling up the entire city. Regardless of this and the fact that he has a huge cape to fill, his promise to the people of his city could make up for all of his numerous failings if he stays true to his word: "My dad served the universe. But I serve you."
This is saying a lot since the whole shrinking-and-bottling fiasco was just one part of a long string of epic failures. In Future State: Superman of Metropolis #2 by writer Sean Lewis and artist John Timms, Metropolis has fallen into disarray so much that Jonathan Kent goes so far as to compare its irreparable state to that of Gotham. Most of the chaos plaguing Metropolis revolves around a Brainiac-derived artificial intelligence known as Brain Cells that can control the minds of citizens who injected themselves with specialized technology.
Then there is Superboy's failure to quell the tensions between himself and the U.S. Army, which wants to apprehend the AI for further study (which he won't allow) and demands that Superboy physically stop the Brain Cells-enhanced citizens from creating havoc (which he also won't do). Superboy feels the most effective way to separate the people of his city who are ensconced in the proliferating chaos and away from Brain Cells is to alter the size of Metropolis and its immediate surroundings. And then he loses all 11 million citizens and all six boroughs to Brain Cells, the very entity that compelled him to act so brazenly in the first place. Luckily, everything returns to normal by the issue's end.
Despite him succeeding, one of the reasons why Superboy's claim that he'll serve Metropolis means so much to the city's citizens is, in part, because of certain events that transpire in Future State: Batman/Superman #1. Taking place before Clark Kent's disappearance, the original Superman finds himself facing the likelihood of death when investigating the mysterious false face serum - and he's not in Metropolis. Although the serum is infecting his city's citizens, he decides to head to the source rather than protect his people by heading over to Gotham.
The issue concludes with Superman at the mercy of Mr. Toad, who jabs a knife infused with Kryptonite into his chest. While it's highly unlikely that Clark will meet his demise at this exact moment, the fact that he could die outside of Metropolis proves Superboy's comment about how Superman served the universe and not just Metropolis.