How Far is the Limit?!

With modern advances in firearms and ammunition components, shooters have been able to keep pushing the boundaries of what is possible when it comes to hitting a target at long range. Growing up with hunting and firearms being a large part of my life, long range shooting has always been the most intriguing to me. While my brother's passion was bow hunting, where the adrenaline rush would come from getting a deer in as close as possible, mine was always the opposite, taking as long of a shot as I could. Now when I was a kid, any shot past 400 or 500 yards was "long range" to me. It seemed that the ultimate achievement at the time was making shot at 1000 yards.
Today a 1000 yard shot would be considered a warm-up to some. With competitions like the King of Two Miles where shooters are reaching out beyond 3000 yards, the bar has been pushed further and further. So what can we contribute this huge increase in long range capability to? In my opinion it's several things.
First of all is the rifle. With advances in machining and manufacturing, rifle manufacturers and gun builders are able to produce firearms with tolerances finer than they have ever been. there are many great options for custom actions and barrels on the market these days. The tight tolerances these manufactures adhere to, when their components are assembled, are leading to tremendously accurate rifles. another factor of the rifle itself is its chambering.
There have been quite a few new cartridges such as the PRC's, Creedmoors, and Cheytacs (for people who like shooting $20 bills down their barrel), that have come to light in recent years. These cartridges are all designed around the idea of launching long, high B.C. bullets a really long ways. With manufacturing technology also brining benefits to the producers of ammunition components, modern ammunition is able to keep up with the abilities of our modern rifles.
So the question still remains... What is the limit? 15 years ago we probably could have never imagined people getting impacts on a target past 4000 yards. At what point are we just not able to overcome physics and have to draw a line? Or do we?