ICBMs already exist. Why the fuck would they add a huge, easily spotted, immobile railroad to that.
The key advancement is supersonic. A supersonic guided missile has the potential to circumvent current (known) missile defense tools.
The space program also serves as a demonstration of capacity and deterrent. ICBMs are not launched at Cape Canaveral, but the launches there demonstrate the nation’s capabilities to the world. MAD only works if your enemies know what you can do.
Hypersonic is just a buzzword without any real meaning - once you’re past the sound barrier there’s no other supersonic barrier to cross. The key is guided. ICBMs were already supersonic, the new development is having missiles that can fly low like a fighter and avoid detection. For that they can’t be ballistic, they have to have enough fuel to maneuver all the way to the target. And to keep size reasonable, you need a launch system that won’t require your missile to have a massive fuel tank just to get going. Enter the new Chinese rocket launcher.
