I honestly don't see the point of most custom frames. They usually strike me as another repetition of something that's been done before. If I were getting a custom frame, I would go for something that really can't be got any other way. I'd be torn whether that would be a modern steel version of a historic frame in my size, or something more radical like a touring frame made for 20" wheels, Rohloff hub, internal cables and wiring, etc.
We have a touring frame in the works that will have a Rohloff, internal cables, and be separable... this is not a bike you could just go and buy off the peg.
This is why I aspire to build frames... to provide bicycles that are unavailable or because your physiology or needs dictate that a custom frame is the best route to go.
If you are average fiinding a bike that fits well should not be a problem since production bicycles are usually built with averages in mind.