"Firstly, there are no “good choices” in Syria today. Qatar has surmised, it seems, that supporting or transforming the Nusra Front, is one of the “least worst” options.
Secondly, the Nusra Front has pledged to concentrate its efforts on removing the Bashar al-Assad government, as opposed to attacking the “far enemy” (ie Western states). On this point, the Nusra Front is aligned tightly with Qatar, which also is implacably against the government and fundamentally believes that the situation in Syria will only improve if he is removed.
This idea is also reflected in the Nusra Front’s composition, which is far more Syrian-dominated than the foreign jihadist-magnet that is IS. This is why Qatar is hoping to bring the Nusra Front in from the cold. If the state can get the group to eschew its al-Qaeda affiliation and adhere to a broadly moderate Islamist platform, Qatar can officially commence, with Western blessing, the supply of one of the most effective fighting forces in Syria."