In the context of an unfinished war and local control by warlords over various regions of the country, while these warlords are united into loose alliances with ties to foreign powers, federalization would mean little more than a neo-colonial partition Syria into zones of influence. From this viewpoint, Syria's partition primarily benefits Israel. Syria, as a geopolitical entity and opponent to the so-called Jewish state, would forever disappear from the region. The United States also wins an advantage and they will try to gain a foothold in Syrian Kurdistan. Turkey, which entered the Syrian conflict with the aim of Syrian partition into zones of influence, would be forced to compete with the US for influence in Kurdistan, and with the Persian Gulf monarchies for influence in the Sunni regions of Syria. Islamic powers will come to grips with each other, the foreign actors will take advantage of this, especially the United States and Israel.
Russia may gain some short-term advantage from such a scenario, as at least it maintains influence over the western part of Syria and military bases. In the long term, the picture is not as good because chaotization in the region that would trigger the rise of Islamic radicalism in Russia itself. Definitely this is bad for Iran: Sunni and Kurdish autonomy would divide the so-called Shia crescent and deprive Iran of access to the Mediterranean through parts of Syria and Iraq under Sunni and Kurdish control, even in case of a victory over the "Islamic State"
The US is actively working with both the Syrian and the Iraqi Kurds, relying on Kurdish nationalism, which is on the rise. At the same time, the Americans do not rely on uniting the Kurds, understanding the role of internal clans, regional and other conflicts between Kurdish groups. Currently, Russia is also trying to win over the Kurds, but Kurds are unlikely to abandon the US-oriented strategy. A foothold in the Kurdish regions, in an area where the border regions of the Levant (the Mediterranean of the Middle East), Iraq, South Caucasus, Turkey, and also Iran all converge, will both directly and indirectly increase the influence of a US supported 'Kurdistan', which is able to win Kurds of all these regions and countries. Israel also is actively working with the Kurds.
A Syrian partition can become a trigger of a defragmentation process for other nation-states in the region. On the agenda are the prospective dissolution of Lebanon, Yemen, Saudi Arabia, Jordan. The disintegration of Iraq will become an irreversible fact. Separatist tendencies in Iran will strengthen. Newly arisen federal entities inside Syria will continue wars with each other, because it is impossible to establish clear borders between different intermingled groups and tribes. Ethnic and religious cleansing will only increase, continuing and escalating in Syria, and later throughout all the Middle East.
The radicalization of Sunni state entities is inevitable. ISIS, or other radicals who replace them, will win because all their enemies will be neutralized and unable to mount any sort of resistance. The number of refugees besieging Europe will only increase. It will change the demographic balance of Europe. The migration crisis will intensify, and so seized by internal problems, Europe will not have the potential to be a geopolitical rival to the United States.
All of this fits perfectly into the American-Israeli paradigm of the "Greater Middle East", which presumes a partition of the region by ethnic and religious boundaries. This plan became famous thanks to the US Colonel Ralph Peters, but long before him this idea was advocated by Israeli military analyst Oded Yinon.
Plans for the federalization of Syria plans are widely discussed by American experts. In favor of this option are Henry Kissinger and Richard Haass, President of the globalist Council on Foreign Relations. The goal of the US is to plunge the region into global chaos, to prevent the rise of Russia and Iran, to weaken Turkey, making it less independent, and to play the role of regional power that will be indispensable in solving any regional problem.
Israel in turn will achieve the aim of weakening their regional opponents. Small terrorist groups and little ethnic and tribal entities involved in constant wars with each other, do not pose a serious threat to the security of Israel as the major Arab states did in past.