Are OTPs approaching custom standards?

Question (and I'm being serious): are there any frame builders who will build you a frame to your EXACT specifications, based on your size? All the frame builders I've seen build frames using standardised tube lengths (i.e. 24" 24.5" etc). Is it actually possible to have a frame built using, say, Reynolds 631 tubing with a seat tube of 25.1" ?

Yes.

If you want this, you can get it. You'll pay for it, but you can definitely get it.