I like the idea of certain aspects of each of those in a Traveller Universe, but there is a fine line between what is appropriate to the feel of Traveller and what isn't.
Here are a few examples that are done well:
Pirates of the Age of Sail - The Pirates of Drinax does a very good job of putting a modern (or futuristic) twist on the idea of pirates. Perhaps, this idea could be formulated and set in another sector with a similar, yet new feel and environment. The step too far would be to have a series of planets that actually used sail powered ships in space (a la Spelljammer in Dungeons and Dragons). As a retro planet adventure, where the characters can travel to a low tech world might make sense, but players can do that now and you'd have to invest a huge amount of time figuring out ways to explains by people don't just swoop down and blow the pirates out of the water with their shiny, high tech spaceships...
Vikings - The Sword Worlds in my mind are exactly what I think of when someone says Space Vikings. Like the Pirates of Drinax it's hard to think how this idea could be reinvented in a way that could compete with the that. Actual historic style Vikings would also be a step too far for the same reasons pirates wouldn't work.
Here are a few examples of things I don't see working well or at all without huge caveats:
Napoleonic Adventures - When I hear people talking about Napoleonic Adventures I assume they are talking about huge land and sea battles. If they are just talking about the feel of French Society during the reign of Napoleon, that's something we probably don't need a full setting about. The problem with huge land and sea battles is that in the Traveller setting each side has the weapons and firepower to destroy entire planets. The wars of the future cannot be fought the same way they were in the past.
Ancient Britain - Knights in armor on horseback jousting to win the love of their lady... Sounds great for a book to read, but without a number of caveats I don't think this is likely to need a full setting developed in the Traveller Universe. In a stretch I could see a setting of armored warriors bound by a code of honor using blasters and swords that might be interesting, but I'd fear that it would be just a pale variation of the Sword Worlds or Warhammer (insert version number here...)
Finally, here are a few examples that are likely worth further development:
Wild West - Basically, any frontier or developing colony in the current Traveller Universe is ripe for a wild west feel. These are remote, undeveloped, and lawless areas where civilization barely has a handhold and survival is far from guaranteed. I'd love to see more development toward this and I think that there is definitely an interest with shows like the Mandalorian, the Book of Boba Fett, and Firefly being so popular.
Outlaws of Sherwood Forest - Remove the Sherwood Forest, add ships, and you're back at the Pirate theme. Remove the Sherwood Forest and change the setting to either spaceports or planets and you're looking more like organized crime - in the future! This could be a winner! I'd be interested in crime syndicates, corporate maleficence, and mobsters - Jabba the Hutt, the Yakuza, Enron, and Don Corleone. Sign me up!
My one new idea is that we've read and know a lot about the Imperium and all the other large governments throughout charted space, but we don't really know much about the groups who are working against those governments. Surely there is some group that doesn't like the Emperor, the Zhodani, or someone else and is working against them. Where are the freedom fighters, the rabble rousers, terrorists, or rebels? What are their stories? What does it mean to live in the shadows of the galaxies largest government and fight tirelessly to burn it down?