Our DADU we are building has a bottom level flex area and bath, then main level open concept (kitchen/living/dining) with bed and bath, and then top level loft with deck and some view.
We looked at townhouses and the trend seems to be a ground level bedroom (or office) with bath, then a main level open concept, then a top level bedroom with bath. The no toilet at the main level was a deal breaker for us.
Op’s idea to separate living and dining/kitchen is interesting and could work.
One of the things you are fighting with separating LR and DR on separate floors is the societal change that seems to be happening. People eat on the couch, in the LR, or on work spaces in the main area area of the house.
Interesting discussion however, as my S and DIL just moved into a similar property in southern CA. They have a half bath on the ground floor plus a sort of useless large entry space and garage with washer and dryer. Second is the great room concept. Third, bedrooms and main bath. But the patio on top has a wall on one side, with a bit of a cover. They transformed the area into a lush garden with seating area, and it has become the coveted spot in this WFH time. I can’t imagine living with all those floors, but it really is rather perfect for the work from home couple.
The Puget Sound area is cooler, but I’d not abandon the roof deck part. Add a wall to protect from prevailing winds, and some sort of heater.
We rented a beach condo in Delaware where the big open concept Living room/dining room kitchen was on the top floor. I agree that a small elevator or dumbwaiter is the way to go. If you can design a ground level bedroom that could work as a home office (separate entrance) that would be great. Families with kids will want most of their bedrooms on the same floor. You definitely want bathrooms on every floor.
On the other hand, some very old (100+ years) people live upstairs. Perhaps stair climbing adds daily exercise that helps them keep their health.
https://www.theday.com/article/20180609/NWS01/180609360
https://www.uidaho.edu/boise/news/featured-stories/research/centenarians
A friend moved to a single level condo after years in a multi story house. She later blamed a needed knee replacement on the lack of stair climbing.
I was going to say that I’d always defer to @coralbrook on design decisions, but I see she answered 
There was a British TV show featuring unusual homes. There was a house build like a tree house. Top floor was the public living space. I believe they had doors closing off the staircase from bedrooms in lower levels keeping them private.
OP again, back with an update. First, my thanks goes out to everyone who participated in this thread; it gave me some helpful ideas.
I’ve been working with a draftsman on the plan, and have just given him the green light on a plan.
Here’s what we’ve come up with:
We’ve expanded the building to three townhomes, up from the original two units.
Each townhouse will have a garage on the main floor and two stories stacked on top. Basically a two story house on top of a garage.
After that, they’re all different. On will have a great room on the middle level and two master bedrooms on top; another will have the bedrooms in the middle and the great room on top; the third will be as I proposed in my opening post: no great room, bedrooms on two separate levels, kitchen/dining on the view side of the middle level, and living room (W/ wet bar) on the top level view side.
Best of all, we’ve configured the stairways identically in each of the plans, meaning that once we frame the exterior walls, stairways, and floors, we’ll be able to check out the views from each level before making a final determination on which configuration to use. Or we might expose them together the market at that point, allowing buyers to choose between the three options.
Wish me luck ?
Sounds great! Can’t wait to hear the progress updates!!!
Thanks for the update. It sounds like a good way to do it. Are you considering living there yourself?
No, we’re building these to sell. We considered keeping one as a second home, but realized it doesn’t make a lot of sense for us.
I like the idea of marketing them as soon as the framing is complete and letting the buyer choose the configuration. I would consider the flipped or traditional floor plan but not one with the kitchen on another floor from the living area. We tend to eat more in the family room than at the dinner table.
Will you have decks?
@dragonmom - That’s exactly what I’m thinking. Frame them, put them on the market, show the three options, and learn what people want. I think the flipped version will be the most popular, but it’s hard to know.
More likely than not these will be vacation getaways as opposed to full time homes, which might make people more receptive to the great room being so many steps from the garage, but we’ll to wait and see.
Similar 3/4 story units along the Hudson River overlooking the New York Skyline. Garage and storage ground floor, first floor 2 bedrooms, 2 baths. 2nd floor master bedroom suite, office, laundry.
Top Floor kitchen, living room, family room 1/2 bath. They rent for 5k month and sell for million plus, taxes in 25-30k per year. In the past 20 years, thousands of these units have been built. There’s literally 50 steps from street to top floor.
Don’t want to forget your car keys ?