I think that any flashbacks of Krypton should show people wearing capes, boots, trunks and chest emblems. Maybe not everyone all the time, but enough to establish Superman’s look as native to Krypton.
Of course, Superman has always worn other outfits during his storied career (as the Man of Steel and as Clark Kent—and in other guises). This would be a worthwhile thread, looking back on all the fashion choices over the 80 years.