Reddit doesn't allow uploading of images or videos in NSFW subs so most of that content is hosted on imgur. I reckon this will be a massive blow against both sites. Not only for the purged archive but also fewer future visitors to imgur when the site is replaced for NSFW and thereby all other content in the long run. Photobucket used to be the goto site. Then imgur replaced it. Another site will replace imgur.

Speaking of old content. That's a massive issue for everyone. Most forums depend on external services for sharing images. This will kill tutorials, progress diaries and close to most images in forums. It's like purging all movies from music predating 1990. It will have a major impact.