As someone who has been relatively inactive in the Pokemon community for several years (and hasn't really played RBY since 2005 or so), this strikes me as absolutely insane.
Looking at the updated strategy dex here on Smogon (and a brief look at Hipmonlee's 2012 article summarizing the metagame), it looks like the game has basically been stagnant for nearly as long as Smogon has existed (which, admittedly, is only around half the age of the games themselves). I'm not sure if I should be bothered or comforted by the fact that there's been basically no new technology to emerge in the past ten years, but honestly it doesn't surprise me all that the RBY metgame was "solved" within a decade of the game's release.
My attitude and mindset might be dated (or just plain wrong), but I honestly am not sure that this makes Chansey significantly better. Sleep and freeze are still valid ways to deal with Chansey (a Blizzard freeze is statistically as likely as two consecutive FP), part of the reason that Chansey has traditionally favored Ice Beam over Blizzard (more PP = more chances to freeze). Thunder Wave (which is already ubiquitous) exists anyway in the event that you do want Chansey paralyzed.
In terms of standard movesets, I don't expect anything to change. Body Slam doesn't paralyze Tauros anymore, but it does paralyze Starmie (and other things that Tauros would rather see paralyzed than not), and even in Tauros vs Tauros mirrors it seems like his best move. If people are really looking for new tech and want to do away with Body Slam on Tauros, my first bet would honestly still be on Leer to replace it. Replacing Body Slam with a move like Headbutt or Stomp seems crazy to me, considering that STAB Stomp is still less powerful than Earthquake. Body Slam is still far and away the ability you'd prefer to have against non-normals (which should be at least half of any player's team) and even against normals, 127.5 base power (after STAB) seems way better than betting on flinches or other silly things. Body Slam is likely here to stay, even on non-normals (I can't really see Rhydon or Golem having anything better to deal with that move slot, and even if they can't paralyze Tauros or Snorlax, they can paralyze stuff like Starmie).
This will undoubtedly affect the way that battles resolve (particularly in Tauros vs Tauros situations; it feels like more of a coin flip since whoever wins the 50/50 escapes with an unparalyzed Tauros), and cases like this don't make the "new" (correct) paradigm seem much more interesting or healthy. (Not that I'd advocate for simulators to not reflect our understanding of the Game Boy game.) The game is undoubtedly different, but I'm not sure it will affect movesets all that much.
This doesn't really affect me at all so I probably have less reason than anyone else in this thread to spend time theorymonning, but it's incredibly interesting to me that things like this are still being discovered, and I feel the need to stress that this development in particular strikes me as totally nuts.