Alloush, here a video of him preaching, was an extremely sectarian man. He called for the "cleansing" of all Alawite and Shia from Syria and he put Alawite women into cages on marketplaces to use them as human shields against government attacks. He praised Osama Bin Laden. Two Years ago Joshua Landis provided a profile of Alloush with some translation of his speeches.
Alloush had many enemies. Unlike other "moderates" he fought not only against the government. When challenged by ISIS, Jabhat al-Nusra or any local competition he fought them too. In the eyes of some Gulf propagandists that made him a "moderate". But his ideologically positions were nearly identical to those of the Islamic State or al-Qaeda. His pasture was the Ghouta area, east of Damascus and he had about 12,000 troops under his command. The Saudis and the Turks paid him and his men.
That the meeting could be targeted is great success for the Syrian and Russian intelligence.
In another success today some 2,000 Islamic State followers and their immediate families left Yarmouk after a deal with the government. Yarmouk is a large Palestinian quarter in Damascus. The men were allowed to leave to east Syria where the Islamic State rules. Heavy weapons were collected by the government and the Syrian army will take control of Yarmouk and two nearby quarters.
These are two very big Christmas gifts Syria received today. While Alloush will be replaced, his "army" is likely to fall apart under any less brutal and charismatic leader. Yarmouk will likely stay pacified for the foreseeable future.
Comment: Alloush was reportedly on the Saudis' payroll since the '80s. According to NSNBC, He was also responsible for the Ghouta chemical weapons attack in August 2013, the chain of command going up to the U.S.'s Chairman of the Joint Chiefs of Staff, the White House, and the Saudi government. He also escorted the UN inspectors involved in gathering evidence after the attack. He had previously been arrested, but was released in 2011 as a result of Assad's policy of clemency.
According to Ziad Fadel at Syrian Perspective, the meeting where Alloush was targeted also included 25 leaders from other terrorist groups, including Alloush's brother, his deputy, Jaish al-Islam's propaganda leader, and the leader of Ahraar al-Sham. The operation wouldn't have been possible without a Syrian Air Force intelligence agent who had infiltrated Alloush's group.