I think you've over generalizing a bit - I think we've gotten to the point where reddit is fairly "mainstream." My bet is there are plenty of reddit users out there not using ad blockers.
There was a time when playing multi-player FPS games against other people on the internet was a "fringe activity" probably mostly enjoyed by a very small subset of the population. Now 40 year old I-bankers blow off steam playing Halo. I think reddit has just about gotten to that level.
If you take a look at /r/popular it's mostly nonsense. The majority of reddit are looking at cute animals and memes about tv, movies, and video games.
People have been proclaiming the end of Reddit since before Digg's downfall.
Do you have a source for that? I don't find it impossible to believe, but that's a pretty bold claim. I'm sure a lot of people use ad blockers, but how does that number compare to total user volume? And how does it break down (engaged users, infrequent visitors, etc.)?
Or I just pay for Reddit Gold, which removes ads (among other features).