I see every format before HGSS-On to be pretty bad and worthy of quiting. I see a very less diverse metagame with only 1-2 decks dominanting. What if P!P even decides to do no rotation and go MD-On that would be a suprise.
Nothing totally bad comes of RR-On, to be quite honest. True, Garchomp C LX/Luxray GL LX are both still in format, but they would then get reduced to tech level play which is far better than this Cyrus Engine set up and gooooooo nonsense that we currently have. If they were to go MD-on, the fanbase would lose faith in P!P, and we would definitely see a very barren season next season.
Barring that, really whats so bad? If you honestly think that there won't be many decks for play, I can list for you a bunch of decks that could still see play with RR-on, even moreso now with Sableye, Uxie, and the entire SP engine going away.
Heres a psuedo-list:
Charizard - Without the ridiculous speed of Luxchomp ruining the format, or the incredibly bad matchup it has with Gyarados being relevant, Charizard keeps HGSS Ninetales as a draw engine and Typhlosion for Energy returning. Not to mention Emboar will be around as well if you desire fire energy rush down. OBVIOUSLY you wouldn't run all of this, but I think you get the idea. (OH BTW DIALGA G WOULD BE GONE TOO), it also helps that it has fighting resistance in a potentially Donphan heavy format.
Donphan - So it loses Uxie and has some minor issues with Spiritomb/Vileplume. Did I mention that Faintgar is out of format? Okay so we still have speed and swarmability for one fighting. GG.
Arceus - Don't even say what. I've seen Arceus in the hands of someone who has played it for months now and he's top cut in every event he's been in barring one cities. This includes TWO States cuts (one a near miss to Dialgachomp in 3 rounds at Top 8) And a cities win. This deck is shenanigans in a 60 card deck box and it loses absolutely nothing next format. I would not be surprised to see this deck pulling off more insanity next season. It also helps that its two worst matchups (Dialgachomp and Machamp) are both gone next format.
Zoroark/Cinccino - This deck quite frankly scares me. Rush down with versatility. Two Stage 1 pokemon with potential to OHKO everything. Zoroark is going to be ridiculously versatile for a long time, being capable of stealing any attack with GoW's and setting up free kills. Combine this with a Stage 1 Jumpluff that can't be countered by your opponent not benching and you have some real shenanigans. Oh btw Luxray GL LX is still in format so the Vileplume argument thats inevitably going to be made is moot. I know people are looking at Emboar. I'm looking at these two.
Emboar Shenanigans - I know people are looking at it, and while my love for Serperior is relevant, I can't say my favorite Grass Snake is going to be at this party. Emboar's output is ridiculous. He just requires some good friends.
Magnezone PRIME - Regirock is gone. However it shouldn't take too much to add some more insanity to this already versatile deck. Creativity goes a long way.
Lostgar - The speed format is over. Lostgar didn't like said speed format. Slowed down format plus Lostgar = Happy Lost Gar.
Turn 2 Grovyle - WHAT DO YOU MEAN THERE'S NO GROVYLES IN THESE SETS?! I CALL SHENANIGANS
These are just a few possibilities. I would be content with an RR-on format, though more content with an SV-on format. The game slows down and goes away from: "If you can dodge a TV, you can play Luxchomp" and returns to the skill-based formats this game once required. I'm not seeing anything after PT-on being bad. PT-on would be the worst possible rotation and I know many people who would probably quit if this were the case. RR-on still has the notable cards, but they're nothing more than techs without Poketurn/E-gain. SV-on is ideal as it gets rid of Luxray and SP radar, which would be the nail on SP's coffin. Blaziken FB feat. Level X would still hang around due to being a ridiculously versatile tech, though, and Staraptor FB as well for also having good tech skill.
Lets also not forget that other sets in BW generation have not been released yet. The shenanigans prior to DP's release didn't really start showing up until Secret Wonders, though Mysterious Treasures had some gems for the slow format (Kricketune and Blissey come to mind.)
I personally want SV-on. But I would be content with RR-on.