Cruise fit for purpose?
Not that I'd ever advocate or support the use of nucular bombs, but I'd have to question whether you could consider a cruise missile delivery system to be a fit replacement for ICBMs. ICBMs have, I presume, a range not less than half the planet. A sub in the Atlantic could lob a warhead to make a glass crater in Afghanistan (or at least in Iraq), I expect.
I can't imagine a cruise having the same range, or even if it does have the range I cant imagine it surviving the trip. A cruise launched from the Atlantic might have to travel over the Iberian peninsula, across the Med, then over Turkey or maybe Israel and Jordan. Someone would surely object in a manner terminal to the missile.