Like most of you, I am not a lawyer but followed that case a bit.
The legal "standard" most gca's are taught to follow is the maddeningly vague guide to design so the "preponderance" of golf balls in normal play do not cause safety problems or conflicts with adjacent holes and property given the totality of distance separation, trees, and other mitigating factors, like trees, the uphill slope at the property line, uphill, downhill, crosswinds, aiming points, tee directing golfers to the fw, etc. Every case really is unique and a deep dive might even consider course type (i.e., presuming more rounds by wilder high handicappers at a public course, and fewer rounds by generally lower handicaps at private clubs).
With all I have studied these things, I don't know what preponderance means, and each case is unique, but the legal system will probably "up" that definition slowly over time by court decisions like the original ruling in this case. (Which was novel, by the way, claiming golf balls and not the humans who hit them were "trespassing" on their property).
At some point, maybe post WWII, I think 90% of shots being contained was probably generally accepted as "okay", but moving forward, I think 95-99 % will be more generally accepted for new projects. I hope it never goes to 99.99% via some precedence in a court case because that is most likely unattainable, and there are probably 12,000 US courses that don't even get close right now.
If the housing corridor contains 90%+ of shots, with about half going wild each way, then the slice side could expect to see 1500 balls in 30,000 rounds. Of course, that will be scattered over 200+ yards and if each house lot is 50 feet, without mitigation, each house lot would statistically still have a ball land on the property about 115 times annually. (Although, a few lots about 160-180 off the tee would only really get that.)
I also understand that while we might measure in % of shots, the homeowner's calculus is more likely to be done on the measure of "balls per day/week/month/quarter/season/decade. 1 ball per X = 183/26/6/2/1 or 0.1 annually for those time periods in a 6 month season. I suspect 1-2 per month would be considered reasonable by most juries and golf course homeowners, but what if that one severely injured their child? Their opinion of reasonable could change quickly.
I have to go back and read it, but either initially or after some remediation this house was getting hit about 15 times per year or about 2.5 per month in a 6 month season. It does appear there were some negotiations on providing reasonably low cost "minor mitigation" (i.e., trees, moving tee back, moving fw away from his house, adding hazards to encourage play further away) but the course owner stubbornly, and IMHO unwisely, stuck to his position that it was not his problem. A bit of cooperation will typically serve golf courses much better.
Also of interest is that much of this comes as a result of self-inflicted changes (i.e., the homeowner clearing his own trees) that neither the architect nor the club could reasonably expect. And, in this day and age, pointing that out will seem like "victim shaming" to many, including those who might serve on some future jury.
I still recall a case in Chicago where new owners of upscale yuppie condos sued to have a 100 year old chocolate factory shut down due to its "noxious odors". They lost, but there is little doubt in my mind that the legal theory of being the first one there reducing liability is slowly fading. There are other cases of suing 150 year old railroads for the noise they cause now that houses are built up against the tracks, and I think some of those have been successful.
It is probably not as big an issue to golf as water and pesticides, but obviously, it is a big issue that may impact any future golf and housing development.