Work with your contractor to find a creative solution. You'll want access to the water shut-off valve(s). It's a good idea to shut them off while you're on vacation. A hose failure while you're gone could do massive damage to your house. It sounds like you have this covered. You'll also want a way to access the dryer vent hookup. If you have to use flexible vent line, at least make it the rigid accordion type and not the foil covered plastic. It should be cleaned once a year or so. If you can't get to it, you'll be tempted to ignore cleaning it. If you have a gas dryer, you absolutely need to be able to get to the gas shutoff valve. These are all solvable problems with a creative contractor. Don't allow them to be so "built-in" they're not serviceable or maintainable.

I think you'll be fine. But how are you going to reach them?

Wall clearance varies from model to model. You are looking at width only. The part you haven't said anything about is the depth. Most of the newer washers are much deeper than the Speed Queen. The depth on the ATE50 is 28". The depth on the Electrolux wave touch (which seems to be a much liked machine on this website) is 31.5" and requires no additional space around the sides and back but needs 1" between it and any door in front of it.

Thanks, rococogurl! I've planned for 1" on each side of the units (total of 29" wide). It's how many inches above that I'm trying to figure out. My stacked W/D are only 70" but I know they won't last forever so I'm planning for increased height of new machines. Good point, though, thanks. My laundry room is so butt ugly now that even if the machine sticks out 8" in front, it's going to be a huge improvement. ;-) But I think I've found a flaw in my plan. I'm going to need a cab side on the right side to support the cab above the W/D. It will be like this (but reversed): So the side of the machines will be hidden after all. My laundry room is small and a walk-through so I'm trying to eke out every bit of space that I can. We meet with our GC to review our preliminary plans tomorrow so we'll see what else I may need to tweak.