I am currently redesigning my kitchen in a 1930’s Midwestern USA house. The kitchen has a decent floor area but the floor plan is oddly restrictive.
My space next to the sink is such that I can either have a standard 24" dishwasher next to the sink and a slightly weird cabinet adjacent to it, or I could have an 18 inch dishwasher at 45 degrees flanked by two small but reasonably sized cabinet doors (or drawers), although the 45 degree plan would dictate a somewhat shallow custom counter depth on the flanks (like 18-20 inches).
I think I would be more proud of the accomplishment of building the angled design, and I think the ergonomics would be optimal.
But I’m not sure about the smaller dishwasher. I have never used a smaller one. It seems like it would be enough for my small family and still plenty helpful for gatherings.
On the concern of replacing an 18" dishwasher if it fails - I see a variety of brands and models from a variety of retailers that are available within the week. The 18" size is not standard but it is also not so rare that I think replacement would be a concern.
I’m sure this will change when I get used to it, but I see a dishwasher as a luxury, I don’t think I’ll be too upset if I have to wash dishes for one week.
I think my main concern is really limited to whether the size is large enough and whether the machines available are of an acceptable quality.
Dishwashers are a luxury, but they also use a LOT less water than you’ll use manually washing dishes and (as long as you clean their filters and use the right detergent) generally do about as well as a bored person doing the dishes will do (ie every now and then you’ll find one with gunk but not too frequently).
Personally, my household has 3 adults and I would go for the full size dishwasher and figure something else out for storage … It’s also possible the smaller ones might be perfect for baking sheets and whatnot. If you haven’t, try to do a mock layout with painters/masking tape and see what you can make fit in that space to try and help with planning, if you can.
With all that said, worst case scenario if no one wants to manually wash dishes, you have to run it twice in one day, every now and then, which doesn’t seem horrible.