Here the would-be rod builder and designer has to trust his instincts.   For example, guide sizing and spacing ought to change if superlines (braids, etc.)  become more prominent than monofilament line. If a braided line has a smaller diameter, less memory, and much greater strength than monofilament, doesn't it make sense that the size and spacing of guides should be adjusted accordingly?  You bet.  But it is going to take a while for the commercial guys to catch up.  They must necessarily market a product with broad , traditional appeal, whereas guys who fish for snook in shallow water have little interest in all purpose rods. Expert anglers want a rod to perform well in a particular environment.
   
To get to this high degree of specialization, the custom rod is the best answer.  Choose a blank according to length and line test preferences, install a handle length that suits you, and experiment with the size and number of guides so that it casts well.  It may take more than one rod, and you might have to make some changes, but if the rod finally fishes to spec, it's worth it.

And that's the reason to get into rod building; strive to make a better tool that is perfectly suited to the way you fish.  Of course, you will also be able to build rods for your friends, do some repair work, and maybe even turn a profit someday.