No, I do not sincerely think Duo and Trowa were switched at birth somewhere in the series. I do however, think their ethnicities were before the show began. While I still say Trowa's ethnicity is up in the air since the show's creators are keeping tight-lipped about it, for this... I'd say Trowa is American. Yes. That is right. After all, why not? I know, I know. "Because Duo is the American!" many would scream outright. Nevertheless, there are some silly, yet interesting things to note about their initial character designs.
In the first opening of the series, we get to see shots of them in clothes that deviate from what they wear in the actual show. Quatre's deviates the most in color and design. Duo and Wufei's lack the intricate designs on their shirts. The coloring of Trowa's clown costume is almost completely different. One might ask, "What does that have to do with anything?" Well, while it is a shame Quatre ultimately wound up always wearing a dark lavender vest, a pale pink dress shirt and pleated pants... The symbols on Duo and Wufei's shirts and the coloring on Trowa's circus costume are rather telling.
Wufei's golden Eastern style dragon is stereotypical when one thinks of China. Well, look at the symbols on the two breast pockets on Duo's shirt. They are golden lions standing upright in an almost medieval European coat-of-arms fashion. When people think of churches in media, they usually think of the Catholic Church. The Catholic Church has strong roots with Europe. Also, consider the additional backstory of how Duo's name originated via Solo's death. The situation could be likened to a plague. The Black Plague anyone? Again, I think of Europe. Duo's "God of Death" alias and the Gothic Reaper motif? I think of Europe again.
Now there is Trowa's case. Why do I point out his clown costume? The coloring of the first design that was never used in the show is more somber, sure... but the color choice is red, white and blue. Sure the yellow is still there, but think golden eagles and the color likened to stars in general.
Then there is the traveling circus he chose as his cover. When you think of the Big Top, the Three Rings, Ring Masters in red tail coats and clowns... What comes to mind? Barnum and Bailey perhaps? There is also the strange similarity in how a traveling circus is full of different characters being paid by performing feats most common people wouldn't or couldn't do to an always on the move mercenary group full of different characters being paid by performing feats most common people wouldn't or couldn't do. Then consider how the Gundam built by L-3 is almost all ammunition, has a retractable blade like an army knife and is colored in bright red and orange like a hunter's safety vest. It makes me think of the United States of America with its obsession with the right to bear arms and hunting for sport. Heck, I just wrote "Bear arms." The Gundam was named "Heavy Arms" with the arms part indicating armory.
Another thing to notice is in promotional art. In the Gundam Wing Memorials ~Final Wing 195~ artbook, there is a series of images fro pages 10-17 where you see the Duo, Trowa, Quatre and Wufei with their Gundams at different locations. The background for Duo's location looks like a European town. Trowa's background is unidentifiable. Quatre's is in a sandy area. Wufei's is also unidentifiable. Strangely, in contrast, when you watch the television opening, there are scenes where the four of them are in their Gundams after finishing a battle. Duo and Trowa's locations are hard to determine. Quatre's location is obviously a desert at nighttime. Wufei's looks to be somewhere Asian when you see the large statue of a head facing his Gundam.
So in the end... What if Duo was originally supposed to be of European descent and Trowa was supposed to be US American? In some ways The United States of America would work well for him, I think. The USA was called the "melting pot" as it is made up of so many different types of people from nationality to culture to ethnicity. Therefore, if Trowa were American his genealogy could be a plethora of ethnicities, giving him an appearance that just cannot be pinned down. That, I feel works well with the ability he was given in terms of being able to blend in so well as well as how his character searches for a place to call home. He really has no specific roots.
So while officially, I do believe the best bet is European. Nevertheless, in the end it really doesn't matter... The sillier side of me does like to think Duo and Trowa were "switched at birth" just before the animation hit the screen, thus the series first opening as well as some official merchandise that follows a similar pattern.
Apparently my strange theory wasn't so strange afterall. I found some interesting information regarding the early stages of designing Heavy Arms from a book called Okawara Kunio Gundam Design Works. It's theme actually was focused on the US of America, the circus and fire. The very first draft looked like a jester, with a montely diamond pattern even! Meanwhile, Deathscythe's theme was on Europe, the Grim Reaper (of course) and wind.
For extra trivia, Wing's design really just had one obvious thing in mind at the beginning: wings. It was supposed to have the concept of Japan, but wings pretty much was its only real theme. Sandrock's design was based on the Middle East (of course) and wind. In time it began to display elements of a serpent via its shield and swords and even wings via the shoulder armor. Shenlong's concepts were China (of course) and water. The dragon aspect was later added on via the Dragon Hang.