I have a hard time imagining that anybody with the resources to secure a nuclear warhead in the first place would later be prevented from using it just because it wasn't plug-n-play compatible with their existing trebuchets or whatever.
It's not about "later" it's about "now". You don't inspect standing stockpiles and delivery mechanisms to say "See? We will never have the capability to nuke you", you do so to show that you're not currently building and are not currently sitting on a pile of nukes.
As mentioned probably two posts up, any ramp up would be obvious to adversaries, have some lead time, and would take away from other production efforts.
