Within the realm of folks who are willing to pay for a Reddit skin, imagine that very few of them will just give up the site once their skin is gone.
More likely is that someone comes in and makes a similar app and charges more for it. Power users and professional users will pay, and most of them will gladly pay a premium.
Not gonna lie… I think op said he charged $10 a year. I raised my eyebrows… that should probably be the bottom option of a three-tier monthly price matrix.
I think someone should buy this app and just price it properly based on value add. Im not sure what the various user profiles of Apollo are, but my guess is that there are a few profiles that can be profitably monetized even with the new Reddit API charges. Imho, Reddit is being shortsighted, but they do have a unique and large community.