This article reminds us of an interesting issue in the creations of counter-factual worlds in Alt Hist - what do the character wear, and what determines whether clothing fashions 'evolve' in an AH world on more or less the same lines as in our own - or whether they are or can be legitimately (and believably) 'fossilised' at the fashions suitable for one particular point in history. In the case of my own alternative version of a Roman Empire surviving to the medieval and Renaissance periods and into modern history, I have wondered whether the 'traditional Roman' elite wear of togas, tunics etc would be retained for centuries as the 'proper' garments for the governing elite, and if this would help to keep fashions lower down the social scale more or less as in the Ancient World. Mind you, the portrayals of Late Romans on mosaics and in book illustrations from the C4th to the C6th show that Roman 'fashion' was not static and long robes and floor-length tunics, often with Eastern-style decorations, had largely - but not entirely - replaced Republican-style togas as formal wear by this period. 'Roman' fashion continues to evolve in the East under Byzantium and the Court robes and Imperial portraits become more 'Oriental' - and the Greek beard comes back into fashion for the Eastern elite as Western and Latin influences fade. So would a surviving Rome have been more 'Byzantine' or would the Germanic 'short tunic and trousers' of those incoming peoples become fashionable?
Notably in Julius Caesar's time the wearing of trousers was sneered at by Latin poets as 'un-Roman', and the Ancient Greeks had regarded them as 'Persian' and 'effeminate' - would this have lasted? Or any Roman soldiers ended up in suits of armour? (Their Late Roman army did wear short coats of chain mail.)
Cf our own world's adaptation of the mid-Victorian 'business dress' suit as the proper and 'respectable' wear for all elites across the world into the C21st, bar a few experiments in the Islamic world with their own traditions , and the persistence of the tie for so long - though it is now loosening up a bit. (And why has women' s fashion moved faster than men's, with the mid-Victorian women's styles long outmoded but the men's still influential in socially elite circles right through the C20th?) There is also the adaptation of the Regency gentleman's outfit for elite social occasions and any 'high culture ' arts events for nearly 200 years on , especially in the world of classical music - I used to think the wearing of dinner-jackets, bow-ties, ballgowns etc for a relatively 'ordinary' and non-upper-class social function like the Booker Prize dinner a bit bizarre and pretentious over 30 years ago, as it wasn't a Court./ govt/ military event. The men's fashions of the C16th to the C18th changed dramatically - why did men's fashion changes slow down after the early C19th? And note the way that even in the late C20th one of the places holding out against any loosening up was the UK Court, with all male royals still in suits and military uniform and banquets with white tie and ballgowns when Tony Blair was in shirt-sleeves on some public occasions.
In matters of AH , we can also note the imaginary 'high society' fashions of the imagined world of the 'alternative American future world' of the 'Capitol' residents in the 'Hunger Games' films. This seems to be an AH 'steampunk' evolution from the mid-C19th, in this case presumably from an idealised past (for the society in the films) from the 'great age' of the US in the C19th - with semi-'Lincoln era' type suits for the men and gowns for the women, plus weird exaggerated hairstyles. Like an off-beat version of the world of 'Gone With The Wind'. Was this from the booksl or an idea of the film's visual stylists?