Almost all NS5A inhibitors are good enough to be workable components of a multidrug regimen. The big question wrt the viability of the 2-drug combo we're discussing is the (as yet unnamed) cyclophilin inhibitor.
If the cyclophilin inhibitor doesn't fly, EDP-239 may not have much of a future; OTOH, if the cyclophilin inhibitor does fly, EDP-239 could be just the ticket to complement it.