Jackie Fisher runs the Star Wars Imperial Navy

How would the Star Wars Imperial Navy change if Lord Fisher were placed in charge after his death?

Only a Fisher given in-universe knowledge and Grand Moff-level authority could reshape it; the result would follow the threat he faced and the regime's willingness to fund and tolerate him.

The counterfactual works only if Fisher gains enough knowledge of Star Wars technology and strategy to perform his new office. Under the former Legends continuity, the coming Yuuzhan Vong threat could lead him toward a distributed version of the Tarkin Doctrine, with no need to build beyond an Eclipse-scale flagship. Under current canon, the absence of that peer threat makes much of the Imperial program harder to justify, while Operation Cinder would probably put Fisher in fatal conflict with the regime. He would also need Grand Moff-level political authority, not merely a Grand Admiral's rank, to turn design ideas into construction. Thrawn's dependence on imperial backing shows that rank and design ideas alone would not secure the ships and resources Fisher wanted.