Well, even the three species listed don't work together. Goldfish (comets) will consume fish if it fits in there mouths. Plecos can be very boisterous when it comes to food and many like meat.
It's been working in this tank for quite some time. I've got Clown Loaches in there too, amongst other things. I got the idea when I was in the U.K. Many stores in London (Picadilly Circus to be precise) had tanks that were built into the exterior wall so you could see them from the street. They had combos of fish I never even thought of in them. The toughest part was finding a good median temperature.
Don't knock it until you've tried it.
FWIW, I got my first aquarium when I was 3 days old, that's right I said "days". I have never not had at least 1 aquarium.
One of these days I'll post the stock list for this tank, it will make your head spin. Don't you fret I have "purist tanks" too.