Maybe they're much better now, but 15 years ago, I used a machine that washed and dried in the same drum, and it was pretty bad at both. A full cycle for one load on minimum settings took an hour and a half or two hours, and the load was tiny in comparison to any other washer or dryer I've ever used. Even if it had taken slightly less time than separate units, and even if the load size had been realistic, I would have had to use two of them to get the usual throughput I'm used to, where I can do a week of laundry in about 5 hours (two people's clothes, bath and kitchen, bedding). If I had to use that machine currently, it would be running for a few hours every day.

The problem with combined washers/dryers is that dryers need to be more empty than washing machines. That means you can either only wash a rather small amount of clothes or you have to take out some clothes after washing and before drying.

My Grandmother had a combo oven / microwave in the 80s. Sears model, I think. It was a full size oven and I believe it ran the microwave part off the 220 connection. The control panel was pretty complicated looking.

It suffered the inevitable result of TV/VCR or TV/DVD combo units where I don't remember which half burned out first but once one half broke it was time to buy two separated devices.