Have you heard of pajama elastic? (Also known as underwear elastic.) This is new to me, but I have confidence that at least a few of my knowledgeable readers know what this is.
It is elastic that is sewn directly to the inside of the pants or shorts - no casing needed. It is usually used for pajamas or other garments where having exposed elastic is not a problem. It is soft enough to be comfortable against the skin.
I'm beyond excited about this as I'm in the process of making three pairs of pajama shorts for my eleven-year-old. This should make the process so much faster (no elastic to thread through casing!) As with all new techniques, my first attempt is a bit shaky, but it's very easy. You make a casing like usual, but you do not need an opening. Make sure your finished casing is a quarter- to half-inch wider than your elastic. Then you stitch along the channels on the elastic. I used this You Tube video from VanillaJoy for guidance.
Have you used pajama elastic for PJs?