It’s reasonable to not want to gamble on the timing—or the ultimate resolution—of an FDA clinical hold. (Just ask anyone who was burned by the FDA hold on CORX.)
Moreover, the FDA hold could cause IDIX to fall to behind INHX and end up in third place in this race. This is a non-trivial concern insofar as IDX184, PSI-938, and INX-189 are very similar drugs.
Another point that you may have overlooked: GSK has evidently dropped its plans to run a phase-2 combination trial of its ‘572 HIV integrase inhibitor with IDX899. Although GSK still appears to be committed to IDX899 development, it looks like GSK has put ‘572 on the express track and IDX899 on the local.