What do you do when a weapon has to be there in 30 minutes or less and you’re not in a position to attack? Send an ICBM…but the target/targets better be really important.
What do you do when the weapon has to be there 30 minutes or less and you don’t want to start global nuclear war? Send a conventional ICBM on a non-nuclear trajectory from a non-nuclear site with a non-nuclear launch azimuth…maybe.
The problem with conventional prompt global strike is not that it will drive nuclear war but that it will never be used given 1) it may never be prompt unless it uses an ICBM or SLBM, 2) it is likely to be really expensive, 3) it’s based on a requirement for exquisite intelligence, and 4) it would rely on a human decision making structure that hasn’t shown itself to be up to the task in all sorts of areas, let alone one of potentially significant consequence.
My guess is the baby will be split: the CPGS “program” will continue along in name without using ICBMs or SLBMs (at low—that is, DoD low—funding rates) to allow CPGS to progress as an engineering sandbox to pursue and grow not-yet-mature programs like hypersonics.