This isn't spoilery in the sense that I know anything. It's just a guess, but I'll put it under a cut just in case...
Several things jelled for me suddenly, and I have a guess at what's happening. At least, it's a reasonable theory. Of course, this is Torchwood, so making sense might rule it out entirely. Anyway...
1. The whole "drug company makes the human race immortal so it can make huge profits selling drugs" never worked for me. And at this point, we know there's a world-wide conspiracy. I have to believe that at least some of the people involved are intelligent enough to realize that they're on a direct path to worldwide financial collapse, which is hardly a benefit to any company. Not to mention... did no one involved in this ever think "what about me and mine"? What happens if I'm the one in an accident, and stuck in a never ending hell with no way out? Or, "hey I'm still aging and getting sick".
2. Why is a drug company involved in planning overflow camps?
3. Why is Oswald what they need now, and Hartley's message correct but coming too soon?
4. What's the "correct geography" that the hit man (did we get a name?) referred to?
So, let's return to old Torchwood, and an old sci-fi trope. Let's say someone discovers an artifact that drains life from one person giving youth, long life, healing, whatever to another. (And an old TW trope come to think of it - gloves and Golden Age anyone.) Now, one person might get away with draining life from people who won't be missed, but even at that, serial killers get caught. If we're talking about a group, esp one that grows to become worldwide, then the overwhelming need is for bodies to drain.
And here comes the immortality device. It might have even been an attempt to create Jack's type of immortality originally, but failed. All that's needed now is to realize how the two could be married. And that is not a simple scenario. It would take a conspiracy with lots of players, and time to get everything in place. Also, and here's where the "correct geography" comes into play, it needs the world in a socio-economic situation where countries would be hard pressed to deal with the fallout. World wide recession maybe?
Once the immortality is triggered, things need to proceed to the point of disaster: overwhelmed health care systems, resources running out, people - even the most caring - burning out under the horror and/or never ending care-giving. It needs to reach a point where someone coming in and saying "We'll take them off your hands. We'll take care of it, and you don't have to worry about them anymore." is hailed as a savior, and no one wants to look too closely at the details. That's why Hartley's message is too soon. Some people may buy in, but too many won't for Triangle Corp to get the unregulated control they need, especially if death returns to the general population. They have to let things build almost to the breaking point so that checking up on the overflow camps isn't on anyone's priority list.
Now I'm assuming that it's not actually necessary to make everyone immortal, but that local fields could be setup instead. Of course, once death returns, well... the people in the overflow camps should be dead anyway, so no one will be surprised if they are. And if mass graves, cremation, etc. were the only way to deal with the overload there'd be no way to trace anything. And no way to know that lots of them are still being held for future use. Or, as an alternative, maybe it's possible to "store" life energy, so the people in the camps are drained before turning off immortality for everyone. Either way works.
Grim enough? So, what do you think?