I would say that 98% (if not 99%) of scuba divers TODAY use a 36 to 40 inch hose on the secondary and donate that regulator (conventional octopus) and have a 22 to 26 inch on their primary.
I very much agree with the general observation. Whether it is 98% or 99%, or a slightly lower figure, the majority of divers I see use what I have come to call a 'standard' second stage hose configuration. Where I might disagree is on the most common primary length, which I see as being ~30", rather than 22-26". But, that is a minor disagreement. Most of our rental regulators, our pool regulators, and what we have sold over recent years to the majority of recreational divers has been a 30" / 40" second stage hose combination.
And, that configuration does 'work', in no small part because true OOA situations really are very uncommon, they occur more often with less experienced divers who generally aren't going that deep anyway, and in those situations the diver(s) ascend immediately and rapidly to the surface (sharing air) without serious consequence. They usually aren't 1800' away from an exit, and don't need to swim single file through restricted passageways in order to get to that exit. Instead, they simply go directly to the surface, even if it means surfacing away from a boat, for example.
Where I will possibly disagree is in regard to whether the situation can / should continue to be improved, even if it has 'worked' for many years. On one hand, there is the oft-cited view, 'if it ain't broke, don't fix it'. It has worked, so why is there a need for any change? And, even if there is a need for 'change', why not focus on better / earlier / more effective gas management training, so that OOAs become unheard of, not just uncommon? Good questions, albeit not necessarily answered by contemporary practice. The needed change in training may be just as much part of a 'scuba board fantasy land', as the widespread use of a longer primary hose.
In the absence of such a successful universal change in training, I elected to adjust my configuration to support what I perceive to be a more efficient / effective way to address the rare OOA situation, that is to: a) be prepared to actively donate to the OOA diver a 'primary' second stage - something that is in a location that I (or the OOA diver) can easily and immediately access, something that I know to be working at the instant that I donate it, and something that is attached to a hose long enough to comfortably allow for air sharing; and b) have then immediately available for my use an alternate second stage that I is (also) in a location that I can easily access, something that I know to be capable of working just as well as the primary second stage I have just donated to someone else, and something that is attached to a hose long enough to comfortably allow for breathing, but not so long that it is either not streamlined, or so long as to make immediate retrieval less efficient. For me, that means putting a second stage identical / equivalent to the primary second stage, on a bungee necklace so it is positioned right below my mouth and can be put in my mouth quickly, or even without the use of my hands.
The question to be answered is what hose lengths are optimal to support those two goals. I can accomplish those goals with a 'standard' hose length setup - I use the (formerly) primary second stage 30" hose for my (now) alternate, and I use the (formerly) alternate second stage 40" hose for my (now) primary. Works well, I don't need to change hose lengths at all. I need to put a bungee necklace on my (formerly) primary second stage. And, I DO need to be sure that i have two identical / equivalent second stages - no cheap, low performance, needlessly 'de-tuned' octos need apply. Given what gear costs overall, an extra ~$100 invested in a(nother) good second stage is a trivial investment.
I can also adjust the lengths of both hoses, if I wish, to improve utility - I can change the 30" hose out for a shorter (~22") hose for my necklace second stage (what the OP is proposing to do). And, I can also opt for a longer hose primary hose (e.g. 5', 7'). That has been my personal choice, and it (7' primary hose) works well for me. If I am diving a wreck, and my buddy goes OOA away from the tie-in point, I donate a second stage on a longer hose, and we swim comfortably back to the tie-in point, and make a normal, controlled ascent. That works for me. But, I also dive a reg that still has a 30" (alternate) and a 40" (primary) second stage hose, and that 'works' for me as well.
Just because we have used a particular approach for years doesn't mean we can't improve (if you always do what you've always done, you'll always get what you always gotten). Just because we have made improvements doesn't mean an older approach doesn't still 'work'.
