I worked at Reddit for several years in the past - if anything, they have the exact opposite of viral momentum: https://twitter.com/paulg/status/1360263618508521480?lang=en
I do agree on the neat alternative piece, but all of the ones that have come up in the past had some sort of flaw (or in some cases deliberate slower growth) that caused them not to go viral (Voat, Tildes, etc)