Just a little thing I’ve put together mentally over the past few years. Nowhere near a properly conducted scientific research- just casual observations.
1st generation– /co/-board members. The first ever Bronies. Being from the 4chan community, they created a lot of the classic memes related to the show (Don’t feed the parapsrites, 20% Cooler, Derpy Hooves). The massive pony bannings led to the creation of Ponychan. Many of these “Old Guard” are still around and some of the “art fags” way back when have served as the fandom’s longest lasting and known artists.
2nd generation– Season 1/Post-Season 1. Spreading interest. Those who were attracted to the show beyond what transpired on 4chan. This is the generation I consider myself a part of. Generally found the show and fandom after its influence started to expand beyond 4chan.
3rd generation– Season 2/Post-Season 2. Between 2nd gen. and 3rd gen., there was a massive influx of furry artists, leading to a massive boost to the artistic talent pool of the fandom in general.
4th generation and beyond(?)– Honestly, I haven’t been able to make too many observations regarding fans who joined here, other than that they keep the blood fresh after a substantial falling out of older fans regarding Season 3, Equestria Girls, and Twilicorn. Without the years of community experience, these fans are generally more embracing of Equestria Girls and Twilicorn.
Again, this isn’t a concrete proven thing- just my own personal observations. Give me your own thoughts!