- "There won't be as many people." That's ok, probably even a good thing. 1.5-2.5 million users are more than enough, especially considering most of them are power users. I believe HN has around 1.5-2.5 million and the content here is way better than Reddit.
- "Making a social network is hard." Yes, but it's not too hard. Scaling is hard, but we're not scaling to Reddit's size (100+ million); and Mastodon has issues with scaling, but that's because their protocol is super-redundant in an effort to be decentralized (and apparently also kind of sucks). HN runs on 2 servers and uses a LISP dialect (https://news.ycombinator.com/item?id=28478379); even though HN is text-only and Apollo would have images or videos, I'm 100% certain there are enough dedicated Reddit users who can make this a reality.
- Also be aware that Reddit's community is different than Facebook, Twitter, YouTube; they're a lot more tech-savvy, a lot more anonymous, favor NSFW a lot more, and a lot more anti-corporate. Especially the moderators, who honestly control most of the community (though it's usually a bad thing). We're going to need those moderators to prevent the Apollo social network from becoming the next 4chan (because, hopefully you understand, that's a bad thing)
There's absolutely going to be an exodus if Reddit does anything non-negligible, the only reason Reddit is even considering moving ahead with these changes is because they don't care.