@KingOfWhiteAmerica if it was an issue of just getting a big payload to the target, the B2 is already good enough, so that alone would not be an impediment to use nukes.

Needing a lot bigger device than that a B2 could carry is a possibility, but what makes you think that this would be the case?
What would be the physical restrictions for the design, and how would that explain some of the geopolitics of today (ex best korea)?