For well over 200 years the banyan was one of the most important parts of any gentleman's wardrobe.
It was meant as informal at home wear, and many a man of arty temperament or leanings had his portrait painted in his banyan, often in his nightcap, or wearing a turban. In the American colonies in the 1700s, and in particular in those states where it was quite balmy a good deal of the time, the banyan even became informal street wear, as well as at home gear.
Why did they fall out of use? Well, as more and more men entered the workplace, including men of title, there was a drop in available leisure time, and the connection with an older way of living and thinking was, I suppose, unavoidable. So by the 20th century the banyan had been replaced by the bathrobe, and the smoking jacket. And the smoking jacket only hung on for about 50 years before it became, itself, an anachronism.
Do I think the banyan could have a place in the modern Attire dialog? Certainly it could. Sure, most men wouldn't care for something in a material impossible to clean, but updated versions could be done that would well serve the growing population of men, (and women, lets be fair here, boys) who can and do work from home.
What say we bring this back? I say lets do this!