Earlier quoted context omitted.
I also have a very strong hunch that the day is coming where this gets deprecated. There will be some kind of big database migration or service refactor, and reddit devs will not want to be messing with that "gross, old legacy codebase" to make it continue working and so the entire thing will be taken offline.
I highly doubt that. Every single time Reddit comes up here, people complain and complain, but also share old.reddit.com as a work-around instead of actually leaving Reddit. It's a perfect way of keeping the hardcore users addicted while having a modern, instant-gratification interface for the majority. They know what happened to Digg, so far I don't see any indication that they're going to repeat this mistake.
It's also sad because even though the old reddit is available, it's not the same. Since all the users are using the new UI, you get a totally different type of user engagement than you used to get I feel. Nowadays it's rare to have any sense of community or long discussion and every subreddit has moved along the spectrum to shallower interactions, image posts, and less distinctive character.