I chose 58" because it's a standard size and appeals to the vast majority of players. I have spent over a decade learning how to make cues at that length, and still have not mastered it. My goal isn't top produce a cue & expect the buyer to get used to it, but rather the player hit the very first ball & experience that WOW factor, knowing they just stumbled into something special. I nail it sometimes, fail sometimes, and do "ok" most of the time. That's with combining all of my experience & knowledge into the effort, and I still don't have it mastered. I may never get there. And that's only 58 inchers where I have the dictation of which woods & where. Heaven forbid I never took the time & made the effort to amass the knowledge that I have, and instead always allowed the buyer to dictate every spec.
If I were to allow the buyer to dictate specs, then all of my knowledge is moot. I must rely on his/her ability to design a cue that will perform well. Then when completed, I have to hope they like it, because it's my name attached to it. If they don't like it, who's to blame? Me or them? How many people will they tell about how I screwed up their cue, that it doesn't hit all that great, or that it's completely unwieldy? Never a mention that it's their design & their specs, only that I don't make a good player. Furthermore, how many of those people will be in a rush to order their own? Zero, none, zip, zilch.
While it's a novel dream to fit a cue to every player, the reality dictates otherwise. Reality says it'll be a nightmare & recipe for failure. Of all the most respected & successful makers, which ones are/were open to the buyer having dictatorship over every spec? Which one custom fit each cue to its prospective player? On the other side of the coin, how many builders who follow that model exist today? And how many have tried that route and completely failed in cue making? Point being, it's a pipe dream. You may be the one who changes it, who figures it out & opens a new door in cue making to advance the craft. But the odds are greatly stacked against you. Chances are you'll flop in no time, ruin your name to the cue world, and never again be taken seriously. That's precisely why the majority of cues are 58".
Having a uniform size that's standard to the industry allows for a collective knowledge base where anybody can learn the nuts & bolts of it, then with their own ingenuity & creativity, contribute their own advancements. Turning that standard into a variable alienates you from the collective knowledge base, making that knowledge useless to you, making your contributions useless to everybody else. The dynamics are new with every change in length. Weight, balance, taper shape, diameter dimensions, aesthetics, everything is completely new with every size you try. How in a lifetime could you ever master the craft when most of us fail to master it only at 58"? Again, it's a cool dream, but once you delve into it you realize it's not sensible. Or at least that's my take.