in my opinion it should be even more in other direction: enemy nukes shouldn't be announced at all unless/when you have intel over them
it's just another broken thing in intel system, giving you free info, similar to knowing when enemy destroys/upgrades a building you scouted 10 minutes ago even if you didn't have any intel over it at the time, because the icon changed color, it makes no sense
and if they moved any slower there would be enough time to reclaim the base before the nuke arrives (yes I already do this on expensive buildings sometimes)
as a counter to no warning given, I suggest nukes should be targettable by anti air fire until they reach space (novax altitude), so air can destroy them until then, once they are in space though, only smd should be able to stop them, even once they start descending to target (hp rebalancing would be needed obviously)