Let's take the easiest situation first: documents have surfaced that show that Israel was talking to South Africa about nuclear weapons in 1975. It's the easiest because the least information is available.
In 1975. That was a different time, and if we choose our facts selectively, we may focus on the fact that South Africa was an apartheid nation at the time. Ugly, but arms sales are arms sales. Anti-apartheid sanctions were imposed on South Africa by the United States in 1986, more than a decade later. And hey, arms sales are arms sales. How many other nations were selling arms to South Africa in 1975?
We now know that South Africa was seeking nuclear weapons around that time. I was working in the laser isotope separation project then, and at one division meeting, for a light diversion, we were told that South Africa, on stationary with gold leaf letterhead, had offered to send a couple of postdocs to the project, all expenses paid. And South Africa has since given up its nuclear weapons and granted full access to the IAEA.
Avner Cohen, who knows more about Israel's nuclear program than anyone else who is talking, parses the documents closely. They are not an offer of nuclear weapons, but the sort of discussion that precedes an offer.
The nonproliferation world of 1975 was far from what we take for granted today. The Nuclear Nonproliferation Treaty had come into force in 1970, and about 90 countries had ratified it, if you include all those (a dozen or so) who ratified in 1975. It was far from the whole world, and major countries like Brazil and Argentina remained outside.
So the significance of the documents is that they show that Israel did have nuclear weapons in 1975. If we want to be picky, we could consider that perhaps Israel was scamming South Africa in the absence of nuclear weapons, but the probability of that seems low.
* Israel was willing to sell the most destructive kinds of weapons to the apartheid regime, which likely would have used them against South Africans.
* Israel has not joined the Nuclear Nonproliferation Treaty.
* Israel's lack of transparency means that stuff like this could still be going on.
Even if these points were fully legitimate, countries hardly ever move because they've been pushed into a corner. The NPT Review Conference is discussing a Middle East Nuclear Weapons Free Zone, and Israel would be part of that. The United States has made some of its nuclear numbers available, and that should be a spur to other countries to do the same.
Although it would make exciting news to report on, it's unlikely that the Review Conference will break up over this or that Israel will come fully clean. Whatever happens will more likely happen in small steps like those that are going on now.