Curious, if BP/W manufacturers considered offering their BP/W pre-assembled in 3 sizes with adjustable harness, adjustable crotch strap, weight pockets, accessory pockets all pre-assembled as options. Pre-assembly could be done by the mfr or the vendor selling for an additional price.
The 3 sizes would have pre-cut and sealed webbing. With the adjustable harness and crotch strap, getting a good fit should be possible without having to cut the webbing again.
If the manufacturer properly marketed this option, would this make a BP/W more attractive for the diver who only considered a standard jacket or back inflate BCD ? I think many divers prefer an off the rack BCD and do not want to bother with cutting and sealing webbing, assembling, etc..
I don't think it's practical for a rig with a 1-piece (of webbing) harness. Any adjustment to the length of the shoulder straps means the waist belt length is changed as well. And that means that (usually) every single D-ring has to be moved.
Doing pre-assembled and pre-sized would really just save people the trouble of the assembly process and maybe having to cut the ends of the waist belt and burn. In the grand scheme of effort required to buy and fit a Hogarthian BP/W, that is pretty trivial. The extra cost to the manufacturer, for the labor to pre-assemble, seems like it would drive up the cost for very little real benefit.
That said, I can see the flip side of the coin. It's not much real, practical benefit, but it could definitely make for more appealing marketing material.