I was only speaking within current VP situation, reducing supply would certainly help against doom carpet but that's another topic entirely.
In term of actual use for nuke there's little that can be done to make it fun, either all in or nobody touching it, thus if you're to put in the effort to make things interesting I would say improving tactical combat would be better, as there're a lot more chance for the changes to actually be used. The changes you mentioned (aside from nuclear winter threat) are also mostly tactical anyway, locking them behind the diplomacy of nuke isn't very nice.
In term of actual use for nuke there's little that can be done to make it fun, either all in or nobody touching it, thus if you're to put in the effort to make things interesting I would say improving tactical combat would be better, as there're a lot more chance for the changes to actually be used. The changes you mentioned (aside from nuclear winter threat) are also mostly tactical anyway, locking them behind the diplomacy of nuke isn't very nice.