I had great, great, great results growing orchids in my bathroom in a previous location. I had a whole wall of orchids--the light coming in through the rather small window was just perfect. So a shower/bathroom is not categorically a bad place to grow an orchid. My mind is focusing on the OP's question about growing the orchids "IN" the shower--and my main concern there would be, the actual shower is a place where many chemicals are used that might not jive with a plant. Soaps, shampoos, etc. Even small amounts of these might be harmful to the plant. I don't know about the configuration you are contemplating so maybe this is a non-issue. But apart from that, if you have the right environment it should make no difference to an orchid if it's a shower or a ledge in the living room.

You bring up a good point about Europe, but there are some key differences between Europe and the US and the way things are handled in Europe vs. the US and you touched on this in your second sentence. And this also applies to antique houses in America, too. Then there is the concept of what is a "natural progression" and I think this concept is something that has not been well followed in the US and that's why there is a problem with "dated". Many people live in houses that are hundreds of years old in Europe. There was no such thing as a "bathroom" in many of these houses for the first couple hundred years of their existence. So, whatever is the first "modern" (~20th c.) bathroom that would have been put in a particular house is always appropriate. And then any subsequent bathroom style up to about 1980. (And not much beyond 1980 or so, imo, which I will get into in a bit). In America, most houses probably got bathrooms in the Edwardian Era up to the Depression, and new houses built after 1900 probably had bathrooms, although I've seen plans without. However, for example, I lived in a building that had no kitchen until 1965, and it had several toilet compartments and probably a room with a sink and bathtub in it somewhere, but not a modern bathroom until 1965. So what's proper in this house? And is a bathroom that was redone in 1955 improper in a Victorian house? Probably not. Really any bathroom that is "newer" than the house (again up to about 1980 or so, imo) is appropriate to the house. Why? because innovations were taking place, and most houses aren't house museums. What happened after 1980 and what is still happening that's problematic in America today? (And maybe not so much in the rest of the world). First, in general, it's one thing to see a very slick contemporary bathroom and kitchen in a 300 year old house, but it's another thing to see a slick contemporary bathroom in a 50 year old colonial revival house. There is much more contrast in the 300 yo house. And what happened after 1980? Up until about 1980, new styles were --new--. the end of the Late modern period was in the 1980s or so and was followed by Post-Modernism which was more or less a statement about reaching an end point in modernism. There is not much left after the white box to pare down. So in the 1980s they started with the fake "Victorian" style bath fixtures and this was followed by revivals of other historic fixtures and elements, and now a prevailing style for kitchen and bathrooms contains a lot of Edwardian and VIctorian inspired elements. It's hard to find a bathroom faucet that is not either a basic style but exceedingly cheaply made; or extremely modern, or faux -Victorian. And that's the crux of the problem: natural progression of bathrooms was always moving forward with technology and new fashions, but now the new fashion is in retrograde, so people are putting in bathrooms that have many elements that are taking stylistic cues from 1910 -1930 more or less in contemporary houses from 1980. It doesn't make stylistic sense. People argue that this is the "current" style going into new construction so it's appropriate but I am not sure. If the current style going into new construction was a bathroom taking design cues from 1955, I think people would see that that looked goofy in a 1980 house. And then there are decorative styles in America that are displaced by geography or are version of something that doesn't really exist. To go back to the OP, there really isn't any such thing as a "Tuscan" bathroom, even in Tuscany. Not how it would be interpreted in America. And while much about the building style may make a bathroom in the Southwest look very appropriate: adobe and or adobe style plaster, wood ceilings, saltillo and talavera tile---that, isolated in a bathroom in New Jersey, when the rest of the house is not that style--again, was never really right, so when that's out of fashion, it looks really wrong. Finally, in new construction, kitchens and baths have gotten larger, more expensive, and higher quality material-wise, than before, and somtimes this is just too elaborate for a house from the middle of the century. There is nothing the matter with improving on quality, there is no need to replace a plastic tub surround with another. But a marble bathroom with detailed nickel fixtures and a crystal chandelier in a modest Cape Cod or rancher just looks displaced. It's the fashion now, so it's what people will do, but it's going to look more dated than something that fit in with the rest of the house better.

In you sketch above, you are prioritizing a separate tub over a decent sized vanity. Perhaps that really is most important to you, but I know we use our vanities a lot more than our tub. Whether your space is 5' wide or 7' wide, you really don't have enough space for separate tub and shower without major sacrifice, like a 24 or 30" vanity. That would be a big detractor for me in a master bedroom. I would either go with a nice big shower, or, if you do a lot of tub-sitting, make a beautifully tiled combo unit with a very nice, deep, comfortable tub. Then you've got room for a good-sized 60" vanity. Much more befitting a new master suite.

I dont consider a separate tub and shower overkill because it addresses the issue of mobility. I no longer use my extra large bathtub because it is too much of a hazard for me to get in and out of with my increasing neuropathy. I designed this particular bathroom with a long large shower I could walk into(no door or sill)that was large enough to contain a bench-very useful when DH broke his ankle. We expected to get old here. The other bath is a miracle of efficient use of space. DH doesnt need to dance in there. I can remember standing in line (7 people) for the one bathroom when I was a kid, In England our house had a separate water closet and tub and sink. You could take a bath uninterrupted but not wash your hands after using the water closet.