I sort of understand this desire. However, I contend that if the contents of the file are important enough that you want to rename the “new X” tab, it is not a bad idea to have the contents saved to disk, even in a temporary folder of some sort.

Have a look at the TakeNotes plugin. Although it doesn’t do exactly what you want, it can quickly create a temporary file (that is saved) with a name consisting of the current time. This file can then be quickly renamed (if you must!) by a right-click on the editor tab (choose “Rename” from the menu that pops-up).