Imgur is already bloated. As for reddit, I'm curious about what makes you think they're drifting towards bloating. They use JavaScript (replying to a comment creates a new textarea), AJAX (posting a comment), WebSockets (real-time updates of comment timestamps), modals (sign up), but they do this in a very moderate way and the result is really robust. It seems to me that they perfectly know the power of all these technologies but have a very strong QA which doesn't let a single shit get pushed in prod.