I have auto update turned off for apps, so I didn't get the last update for Infinity and I can still use it to see Reddit, for now. Once it dies I'm out though. I can't imagine they will be able to get enough subscriptions to support the app, so I'm not really sure what the goal is here.
The Infinity listing in the Play store links to this post that has a bit more info (warning: Reddit link) https://www.reddit.com/r/Infinity_For_Reddit/comments/147bhsg/the_future_of_infinity/
Even the people subbed to r/Infinity_For_Reddit are saying they won't buy a subscription. Wouldn't Infinity be racking up a huge bill from Reddit once the API change goes into effect? There's no way subscriptions will cover that so I don't understand why they're doing this.