Mike:
Nothing really "wrong" about your ideas, although I'd add these thoughts.
Your list of hypotheses:
1) Short, 3-4K drains will limit engine damage and sludge buildup in the event of coolant leaks that occur in between oil analysis samplings.
2) Short, 3-4K drains will limit abnormal engine wear from dirt ingestion due to an air filter or intake system leak.
3) Short, 3-4K drains will limit abnormal engine wear and extreme viscosity change in the event of a severe fuel dilution problem.
4) During a short drain, higher levels of detergency present in the oil may lead to fewer solids, varnish, and deposit buildup.
5) When an oil filter is run for a short period of time, there is a lesser chance of filter failure.
As to 1) and 3), whether or not you catch such things in time will to a substantial degree be a matter of luck. Either fuel or coolant being where it shouldn't be (in the oil) could very quickly kill your engine (but slow leaks might mean slow death too, and if so, 1 and 3 make a lot of sense). And many of the folks who follow the short OCI program justify it in part as a way to avoid having to bother with UOA. If you did do UOA with every 3/3 change, and you were lucky, both would be correct.
As to 2), if you're in a very dirty environment, all bets are off. This from a hard-core syn guy; use good dino and change often, if you're not going to test. Also, regular short OCI would indeed catch a sneaky intake leak that was letting bad stuff in unseen. There are risks and benefits in any approach, and I suppose this would be one of the risks of the long drain approach. Personally, I tend to my own air filter, which in a G35 can been clearly viewed in its installed location through the supplemental intake. Changing it, however, requires substantial manipulation of the intake plumbing. I'm careful with it, and inspect it often for just that reason. I hope that's enough. . .
As to 4), at least with my vehicles and usage, neither my UOA nor the view into my engines seems to indicate that I've crossed the threshold of inadequate detergency. Think of oil like dishwater. New dishwater looks and smells pretty, but it really does not clean dishes any better than half-used dishwater. When the suds are gone and you can feel grease on your hands, though, you know it's past time to change.
And to finish, let me beat on poor old Fram for a moment. Despite the awful reputation (amongst those who know) of the paper end cap specials, really, how often do we hear of them actually failing. I've heard a few stories, but no widespread meltdowns as far as I can tell. That said, I'd never use one. Use a sturdy filter from a reputable maker, and the probability of filter failure is extraordinarily low.
In the end, however, you should only go as far as you are comfortable going, all things considered. For many, there should be an item 6) on your list, which would read, "I just can't let go of the short OCI no matter what I learn. . ." That's not a slam or poke in the eye. If you feel that way, that's fine. In most cases, though, people can take their oil a good bit further than they actually do.
