I think all the comments to date are spot on. I'll add this wander;

My gut feel is that the outcome of attempting to make a bike that will do two rather different things is a bike that really isn't very good at either. The real 'oh my, oh my, OMG' moment of a truely nice custom fitted bike is in finally having a bike that fits you so perfectly, rides so exactly the way you always hoped to be able to do someday, and is so awesomely responsive that it seems to drive and steer itself where you wanted it go without even needing to consciously think about it. Your current approach, I suspect, will end up with you spending for that bike, but missing that moment. That would be a loss! Sort of like not showing up for that 4th date with a supermodel!

Best recommendation would be to have a serious long honest ponder on which type of riding you really enjoy the most and will do the most...and then get that custom bike for that specific purpose. Then just add an adequate rack bike to do the other job for a while. If luck smiles on you, sometime not too far out you may be able to get a really good custom bike for that second purpose also!

To be complete in life a real biker/cyclist needs a custom MTB, a custom touring bike, and a custom tandem (with the super model stoker...of course).

If above brings a tear to the eye...please deal with it discretely!!