Apologies that I'm on my phone right now and don't have links at hand, but I have done some reading on this topic recently.
From the conclusion:
> Intubation rates did not exceed 35% in non-ARDS and mild ARDS and NIV may thus be used as the first-line ventilatory support ... By contrast, 84% of severe ARDS required intubation and NIV does not appear beneficial in this subset of patients ... In patients with moderate ARDS, NIV may be worth attempting in those having a PaO2/FiO2 ratio >150 in the absence of hemodynamic instability or altered consciousness ...
There are definitely significant shortcoming to that study (single facility, etc), but it definitely points in the direction of CPAP being a viable treatment, especially if it's used aggressively (initiated early, high PEEP, etc)