The placement of the washer and dryer in a house should be considered
permanent.

Well... permanent? I'm about to move them aren't I? Once I move them
are the appliance police going to make me keep them there? What if we
change our minds and having a working mudroom doesn't pan out, and we
decide to move them again? I will if it makes sense again.

The carpet under the plywood or pan under the washer and
dryer is lost anyway.

It never occurred to me that the carpet would be ruined from this.
Carpet seems to survive furniture... and because furniture generally
has a smaller footprint, I has a fairly high pounds per square inch.
Sure it looks crushed at first, but over some time and vacuuming... it
comes back. Why won't it in this case? I'd have to do some math to
find the full load weight versus the footprint.

It's your house. Arrange it to suit your own
circumstances and needs - not those of some possible future buyer.

Although a toilet might be convenient as a night stand... I'd warn you
that I won't be buying your house if I find this.