I'm not a webdev so I understand if this point is naive. The Apollo dev said the cost will be about 20x what Reddit pays for its user. Obviously Reddit needs and can maintain a competitive advantage by having a native app. So charging more per user for a 3rd party app is not unreasonable. For the sake of simplicity let's say that reddit makes $1.00 per user per month that uses their app. Currently they make no money…
It seems that the Reddit executive team has decided that killing third-party apps is in its best interest regardless of the probably-to-some-degree-expected backlash. I think Christian's and your conclusion, that Reddit intends for the new pricing to be prohibitive, which indicates that it "is obviously intended to kill third party apps," is fair.