I think the riffs are more "generalized." In the original, there were riffs that were regional or more obscure (e.g. Hamdingers).
At this point it sees the fans are split into people who follow whatever MST3K and Rifftrax do, “keep sharing the tapes,” and people who liked MST3K because it was funnier and scrappier than other shows and tapered off when it lost that. I lean toward the latter, but I’m friends with the former and we make it work.
(And happy "thousand" got shorted to "K" — perhaps the early USENET nerds coined that.)
IIRC, they might have been crowdfunding for a fourth new season, but they ran into some major issues with getting backers their rewards on the last one, and I think that made a lot of fans reluctant.
Note also, there's another season that's on the streaming services as individual movies post the Netflix reboot with much of the same team.