There is, or was, a minor trend involving blouses with decorative elastic ribs sewn onto the front panels, such that the front of the blouse was divided into wide vertical strips of narrow horizontal crinkles. Since I know about it, let's assume the past tense is appropriate. Presumably, the purpose
of this arrangement is to emphasize the wearers breasts.
(Does anyone know what I'm talking about? I was hoping there would be some witty marketing name for the practice, but my ill informed attempts to google for it turned up results that were... diverse, and mostly wildly innapropriate.)
The material of the blouses is generally, I believe, somewhat stretchy itself, but there is an obvious potential here to facilitate movement in relatively inelastic fabrics. I would like to see this technique applied in the following areas:
1. Above the kneecap, and below the buttocks; to allow sitting or squatting without drafty ankels. Useful for people who's socks never match, and plumbers.
2. Below the armpit or inside the bicep; useful for raising the arms overhead, without raising the cuff or exposing the midriff. Useful for people with unattractive underpants. (been sone, see link)
3. Across the shoulder blade, outside the bicep, or over the tricep; allowing one to reach forwards without raising the cuff. Handy when you have tucked your sleeves into, say ski gloves.
4. The inside of the thigh, to allow for a vide variety of splits to be executed spontaneously, in jeans or slacks. The appeal of this is probably limited to a small market consisting of, say, Jet Li.
The pants could be done by adding short vertical strips of elastic in helix, beginning outside and below the hip, wrapping under the buttocks, around the thigh, and terminating above and outside of the knee. For the shoulder the elastic could extend radially from the shoulder joint, beginning below and forwards of the armpit, passing under the armpit, and rising over the shoulder blade. Many other patterns are possible, being equally functional, and providing flexibility in meeting aesthetic considerations.
I believe there is a capacity here to improve the comfort and ease of daily life, using means of little cost or complexity; which is, after all, the universal aim of fashion.