From what I can tell, the idea didn't really take off in rest of America, but Hollywood designers and stars loved it. When the leading lady appeared dressed in hostess pajamas it meant that her character was glamorous (ball gown), slightly bohemian (pants), and sexy (split-to-the-waist overskirt), or, and this is a big or, it could mean that her character was just pretending to be all those things. For example, in Imitation of Life Lana Turner (shown here in an unrelated publicity still) wore hostess pajamas, or as I like to call them, glama-jamas;
Lana Turner: you'd better believe she's glamorous
A search for "hostess pajamas" on google yielded more hits for Barbie clothes than anything else, so you know they had to be hot:
What, you were expecting Barbie to wear a snap-front house dress? As if!
And you KNOW hostess pajamas had to be super glamorous if they were featured in a Modess . . . because ad.
Because she's hot, that's why!
On the poser side, Judy Holliday wore them in Pfffft (I've never seen it either) and Born Yesterday, and Lucille Ball (not pictured) wore them on I Love Lucy.
Judy Holliday and Jack Carson in Pfft.
Judy Holliday, Broderick Crawford, and William Holden in Born Yesterday. The plot in a fashion nutshell, she gets smart and loses the glama-jamas.
As Hollywood glamour went out of style the ball gown version of hostess pajamas disappeared in favor of palazzo pants and other simpler, saner, clothing, but designers were and are always trying to bring back the dress-over-skirt and pajama dressing. Both these trends were out and loud at the Met Gala so that we can (a) understand why this garment was supposed to be worn at home, (b) recall what a ridiculous and often unflattering ensemble it is and (c) separate the truly glamorous from the posers, or not. Observe:
Sophia Coppola in Marc Jacobs, with Marc Jacobs. All pajama, very little glama, but at least she's prepared to take a nap if things get really boring.
Sara Jessica Parker in custom Giles, with custom Louboutin boots. Lotsa ball gown, very little jama, but she has to be wearing some kind of pants under that thing, doesn't she? For the love of all that's holy, DOESN'T SHE?
Jessica Biel in Giambattista Valli Haute Couture, with the designer, Giambattista Valli. Jessica looks a little worse for wear in that photo, so it's appropriate that she's wearing her glama-jamas derelicte.
Jessica Paré in Jason Wu with the designer, Jason Wu. Jessica's outfit is probably the closest to the Hollywood original; I could see Lana Turner wearing it, but I wouldn't like it on her, either. Damn that 1980s blue. And girl, the eye make-up? No.
Doetzen Kroes in custom Theyskens' Theory, with the designer, Olivier Theyskens. Something got lost in translation and Doetzen wound up in a skirt over a skirt, both slit up the whazoo, but she's hot, the leather over-dress is kewl, and Olivier Theyskens is as cute as a button, so who cares?
Hilary Rhoda in Wes Gordon. Now would that be business in the front and party in the back, or party in the back and business in the front?
Gaia Repossi, in Dior Haute Couture. If this is the new Dior Haute Couture, then LVHM needs to hire a sobriety coach and bring back John Galliano right away. (I bet that crazy little dude could design the shit out of a pair of glama-jamas.)
Elaina Watley in Naeem Khan and Victor Cruz. This one, I like. It's tuxedo-ish, which is always a winning look, the overskirt and pants don't clash and they're nicely balanced.
I think the lesson to be learned from all this is that if you have the urge to wear glama-jamas, stay home and watch Lana Turner and Judy Holliday movies until it passes.