I'm a big fan of custom-made clothing (I'm an engineer at ThirdLove [1] - you take a picture of yourself, we figure out your measurements based on the picture, and you can buy clothes from our vertically-integrated brand based on your fit). Maybe I'm a pretty standard size, but is there really a huge demand for custom-fitted t-shirts/henleys? Custom fit is valuable for clothing that is three-dimensional (suits/sports…
The reality is that many people are served really well by standard sizes - but there are huge pockets of people that aren't, and that traditional retailers choose not to accommodate. We're not doing completely custom clothing eg. an all together different pattern - we'll do it, as a service if none of our sizes fit, but I think that is pretty unlikely.
What we've done is taken the most overlooked body types - tall and thin, extremely athletic (body builders etc.), and heavier-set guys that want nice shirts, and built sizes that look good on them.
That said, I DO genuinely think that our medium shirt (the size I wear) fits better than any medium I've tried before. We've had a TON of feedback to confirm this.
Great advice on the checkout forwarding. Will definitely make that change soon!