I mean, do you really care if people think you're advertising at this point?
luna
You can handle growth, but you need to be strict about moderation, and a lot of people don't want to do that for some reason.
You overestimate how many people use third-party apps. They are the (very) vocal minority. They may represent a majority of the content submitted, but there's an arbitrary number of web users who don't have an account (hi) in addition to all the casual users who just use the app.
I'd love to see more communities that cover topics outside of the usual STEM / STEM-adjacent / typical redditor interests. I was on another reddit-alternative a few years ago called tildes and it was ... shockingly like a microcosm of reddit. Like, it's hard to describe how narrowly-focused, how stereotypically reddit, the userbase's interests are. STEM, anime, gaming.
The music, literature, humanities, environment, city life and so on communities are excellent starts in that direction. And, despite the fact I'll never read anything there, the sports community is equally valuable for the same reason.
That said, something for tabletop games would be cool, too. Preferably something not D&D/MtG because we all know they completely take over every space they touch (like my FLGS... RIP).
The thing is that askhistorians is, uniquely among subreddits, both staffed by professionals in the field and heavily moderated. It is an investment by credentialed, dedicated professionals, and would not work otherwise. I think something like that would be highly attractive, but I caution anyone against trying to resurrect it without access to those credentialed, dedicated professionals. Otherwise it becomes shittyaskhistorians but unironically; at worst it would be ancient aliens.
Beginning to? No. That happened years ago. It was clear several years ago that they were taking the site in a direction I didn't like. Around the time that "new" reddit was released along with the official app.