wow, a poor layout, for sure. Do you use everything in the space?

If you eliminate the tub you would have room for a w/d.

Do you need a rug under foot? a bathmat in front of the tub only when needed, otherwise, drape it over the edge of the tub.

one in front of each sink/vanity for warmth on cool mornings.

Past poor and on the way to really bad . That layout is awful . I see no point in trying to add a W/D to this mess . I would need a ton of info to even begin to help So start with a to scale floor plan of this space and the others around it . Then tell us what you would love if at all possbible Then we can start

That’s validating that it’s objectively awkward! It feels cavernous and cold, hence the interest in a rug. We dont use the tub, but we do like the separate vanities. What is the least and cheapest changes we could reasonably make (not DIY!) that would give us a bigger closet that could include a washer and dryer?

move the toilet and shower closer to the vanity area(s)

depending on the size of the windows near the vanity(s)

I would extend the closet area into the tub spot so you have a window in the closet.

Add the W/D where the Toilet is now. (you already have a drain and water source.)

remove all the interior walls, access the closet from the bedroom, not open to the humidity of the bathroom.

Take the plan you posted, add the master bedroom, and any hall passage.

Get a measuring tape. Every solid wall, every doorway, every window, has a dimension. Add those dimensions.

That's how you get a PLAN.

How long have you been in the house, how long will you remain in the house, what would a "budget" look like? $$$$......???

Is this second floor or ground floor. If ground, is there a basement? Or you're on a slab?

Add jpegs of the entire suite all the angles.

Do you USE the tub frequently, or rarely? Is there another tub in the house?

See what I mean?

The more information, the more accurate the information?

The better and more accurate and "possible" the answers: )

"We're daydreaming about adding a stacked washer and dryer, but I need to see how much it would cost to accommodate a new vent.".........

That is the least of the issue: ) and the cost