Well, we can't stop you from creating a new city if you want to.
But, personally I would not like you to start a new, unused city, only because all of your Rare items will be lost,and your memories from the city will fade away.
Lol, I did this and my town now is coming along better than my first one. Caught 4 coelacanths, have a better museum, have better villagers, and the list goes on. You might wanna consider..