The format of the story i.e. a ship is not as important as the characterisation and overall writing. After all DW is almost 50 years old, and how is the core story different today that it was in the 1963-1989 era? What's really changed Is still more or less about a renegade alien having adventures with his companions. Or "The Adventures of a Mad man and his Blue Box."
I know Janeway destroyed that localized Borg hub, but aren't they still out there? Perhaps the Borg are also assimilating other galaxies. If Star Trek is really confined to the Milky Way, then what opportunity do we have to see another series?
Trek isn't confined to our Galaxy, it's just that our Galaxy is still a really big place and even with warp drive, the vast majority of it is still unexplored and unknown by the late 24th-Century. In the Star Trek Universe, there are potentially several hundred billion star systems that have yet to be visited (taking into account three dimensions). It'll take awhile to see them all, IMO...