[nessguy]

While I don't know of any washers/dryers with them, heat pumps can be more than 200% efficient, so there's still potential for improvements there in theory.

Though to be honest I agree with your point. A lot of the low hanging fruit for massive gains in efficiency are gone. It's like cars, going from 10 mpg to 20 mpg is a huge difference. Going from 50 mpg to 60 mpg is a much smaller difference.

[ClumsyPilot]

"While I don't know of any washers/dryers with them, heat pumps can be more than 200% efficient"

But then the washer is stealing heat from your house? That seems questionable?

Seems like the right way to solve the problem is to provide hot water inlet, and that should provide it is whatever most efficient way you can?

[maxerickson]

Heat pump dryers don't exhaust air to the outside, which saves a lot of energy relative to what is pulled from the house.

(The water is either collected in a container or goes down a drain)

For modern top loading washers, the final temperature of the water is restricted by limiting the hot water let in, they don't have a heater.

[coryrc]

Heat pump dryers are common in some places. Don't believe heart pumps are ever used in washers though.