While Krennic could be released at the same time as Scouts, wouldn't make much sense. We never saw him directly with them, especially when the Deathtroopers were his personal troops. FFG so far has kept the additional releases with some sort of theme (Veers & snowies, Leia & fleet, Endor Han and & commandos). Blaise makes the most sense for a scout team, albeit slightly boring for a commander. It all depends on how mirrored they want to release the sets. If Rebels get snipers, do the Imperials have to get them or can they get a different utility with their special forces? I'd personally like to see some difference between the factions so they feel like two different armies.
This is going to be the hard part of filling out armies for FFG. Imperials have great units, lack of solid commanders. Rebels have great commanders but a serious lack of units.