Private key harvesting apps, which turn accounts into automated spam bots.

Something like that could be a real risk if it became popular.

Assuming the individual(s) behind the app(s) are thinking long term, a handful of their apps get semi popular and harvest a few thousand private keys each over a matter of months or years.

Then one day, our entire feeds are full of advertising or gore or something and a large number of people have to restart building their accounts.

That's the biggest risk i think.