I imagine more of a retrofuturist aesthetic overall, with an Art Deco touch, though perhaps Coruscant’s architecture would be more Gothic, in keeping with Ralph McQuarrie’s concept art for ROTJ. Everything would be cleaner and in better condition; not much of the OT’s “used universe” aesthetic would be in play here, except in the seamiest of places. Imperial and Rebel ships would’ve evolved from earlier Republic designs; think first-generation Star Destroyers housing pristine Y-Wings and Z-95 Headhunters. Mon Calamari and Quarren wouldn’t be around, as they didn’t make first contact with the greater galaxy until after the formation of the Empire. Korriban and perhaps a few other planets from the ancient Sith Empire would logically make appearances.