They may've been to every quadrant, but they've explored only the teeniest possible percentage of all that space--there's really nothing keeping them from setting a new show in the future of the Milky Way, if they want to. The voyage to a new galaxy idea works, too, but it'd just be sorta unnecessary, I think--and, besides, it'd keep them from using any iconic locations from the series' past, which'd be a bummer. I'm just wondering if they'll keep the destruction of Romulus canon or not--even though it technically happened in the Prime Timeline, it's never been referenced outside of the Kelvin Timeline films, so... I dunno, there's some leeway there, I think. (Honestly, I'd be up for them dumping pretty much all of the TNG films - I hated Generations and Nemesis, like, a lot - out of canon, but I know it'll never happen.)
Anyways, in other news, I just got a package in the mail...