The intelligence estimate casts doubt on the likelihood of a full peace settlement materializing in the years before 2020; nonetheless, should an Israel-Palestinian agreement for a "cold peace" win support among a majority of Palestinians, it would constitute the most significant development in the region since the establishment of the State of Israel in 1948, improve the Arab world's attitude toward the U.S., and eliminate a pretext used by Arab countries which are reluctant to implement political reforms, the U.S. assessment claims. Israel, the evaluation adds, will not relinquish nuclear weapons it possesses.
The Middle East section of this global assessment warns about the possibility of a war between Israel and Syria, or some other Arab state. In such a future war, it is possible that unconventional (biological, chemical or even nuclear) weapons could be used, warns the National Intelligence Council. Such a war would eradicate the softening of Arab attitudes toward the U.S., and also derail efforts to revive progress on the Israel-Palestinian peace track. Another rout of an Arab army by the IDF would cause Arab populations to reconsider the viability of their political regimes.
Surely that was the argument about 1967, but even the viability of Arab political regimes was doubted, there was little opposition movements could do about it, particularly while these governments became clients of the US or USSR. I also wonder if the 2020 date is perhaps a reflection of wishful thinking -- certainly the current Israeli government does not seem interested in achieving peace and thinks time is on its side (which has been more or less the policy since 1967, since time allows the creation of facts on the ground.)
You can download the full report in pdf here and take a look at reports for other regions at this page.