It's baffling to me that Amazon doesn't have something like this. Every vendor of clothing seems to upload a size chart or puts it in the text description, and you wind up with stuff like "6x plus size dress" having a waist size of 32 inches.
I don't understand why someone can't put in a few basic measurements - waist, hip, bust, inseam - and filter clothing based on those, today. It wouldn't be perfect, but it'd be a damned sight better than putting "plus size dress" and getting keyword-stuffed listings made for a size 0.
The jeans, not so much (they still need to work on it), but for shirts they were spot on. I will never buy 'off the rack' shirts anymore.
Everyone has different fitting issues. My main one is waist length/width and shoulder width. I'm 6'2" and fit so the waist of most shirts barely go below the top of my jeans and getting the shoulders to fit often means having a parachute around my waist. It looks dumb and clothing fit is extremely important to overall appearance. There's a lot of disruption to be had in this space.
Edit: to be slightly more clear, I'm thinking of technology to replacing the incumbent infrastructure/processes/consumer experience, as opposed to just creating a new specialty brand.