Beth, I agree that it could be a mistake to build your cabinets so that the only w/d possibility is stacked, b/c with 3500 sf, you're looking at resale to families with kids--hence TONS of laundry. And most people buying homes (at least of that size) already have their own w/d, so locking your laundry room into a stacked configuration would definitely be a negative. Side-by-side units give you the whole top surface for folding, esp. if they're front-loaders. Just don't get the pedestals underneath if that's your only folding option, b/c the w/d get pretty tall if you do (great storage, though, if you had a counter for work space). Depends on how tall you are, I guess.
Does that help? Front loaders w/o pedestals = nice work table across the top, too (I'm on the tall side & never had a problem w/the height). I think you're asking if you should configure your l'rm to have cabinets that'd accommodate stacked units--? I'd say no.
If you're afraid of butter, use cream. ~~ Julia Child
As you cook, you enjoy omniscience about food that no amount of label reading can match. Having retaken control of the meal from the food scientists, you know exactly what is in it. (Unless you start w/cream of mushroom soup, in which case all bets are off.) To reclaim control over one's food, to take it back from industry & science, is no small thing; indeed, in our time, cooking from scratch qualifies as subversive. ~~ Michael Pollan