Apollo Apollo (well known iOS client) developer talking about the specifics. Sounds like the API will now be paid based on usage.
It's a bit easier to have an opinion after the Apollo developer revealed the specifics Reddit gave him. Other than the NSFW part, which seems odd considering the API will be one of the revenue streams that isn't advertiser supported, it seems reasonable, of course waiting on the final price per usage.
It was never going to be sustainable for Reddit's API to be fully free. It was just silly - you could use the whole site, which certainly costs money in both AWS fees and developers doing KTLO, and not see any advertisements via the API.
App developers will pass the costs along to the user, many will likely fold because it won't be commercially viable with the additional cost, but, well, that's the way of things.