The only problem with dual faction ships is getting LFL/Disney to sign off on them. They may never approve of giving the CR-90 or the Neb B to the Imperials since they're somewhat iconic for the Rebels.
I could see a new ship that's dual faction. But I also think they'd have be running low on options before that's likely. Out of all the ships in X-Wing 4 are dual faction, and none share between Rebels and Imperials.