It will likely never be known what compound, but the "spray bottle" tells us that the agent was targeting respiratory system, not dermal. However the use of V-Series agent is a strong indicator of military assassination as almost all research on these chemicals is confined to secret military research. The Russians have admitted to the synthesis of more than 100 more novel V-series nerve agents.[1]https://en.wikipedia.org/wiki/Novichok_agent
While I'm not convinced a binary compound was needed in this case, it is an interesting theory!
"the "spray bottle" tells us that the agent was targeting respiratory system, not dermal. "
I'm not sure this follows. If the cloth was impregnated with one of the binary components and the other was sprayed on the cloth, then VX would be synthesized right there in contact with the skin. I don't know that you could be sure a lethal dose would be inhaled in one or two seconds.
I imagine NK is the sort of regime that doesn't have moral qualms about testing this on, say, political prisoners, before using it in an actual assassination attempt.
While I'm not convinced a binary compound was needed in this case, it is an interesting theory!