I'd say when the meme is featured. Otherwise it might be too much. In fact, if we were to actually implement this, it'd probably have to be simplified to a page with a list of links to the profiles of the users of your choice. Too many notifications... augh, Facebook flashbacks! it burns my eyes!!
Anyway, I'm aware that bookmarking profiles is an option; however, I'd like to be able to organize said bookmarks, and Chrome is the only browser I've used that, to my knowledge, can have bookmark folders. I'm a Chrome user most of the time, but if that wasn't my browser of choice, I'd probably find it annoying to have to download another browser just so I can have my imgflip-related stuff organized.
Finally, I don't think the slippery slope will get that bad. This is just a proposal to have a convenient way to access your favorite users without having to bookmark each profile individually and or write them all down somewhere, you know?