The recently established Tiering Policy Council has been talking about this for the past few days and we've decided that going forward, the final two shifts of a generation will only feature drops and not rises. We've all read every single post in this thread & Meri's similar thread, so here's our justification.
While we understand some counterarguments (i.e. lower tiers getting potentially harmed near the end of a generation is just the nature of usage-based tiering), we all collectively agree that as a group of fans striving solely to have the most fun we can with our metagames, it is undesirable to have any of them left in a disliked or potentially even near-unplayable state. Situations like SM PU Mesprit are somewhat rare, but they are also very unfortunate and completely avoidable; there is no real reason for a playerbase to need to "fix" a tier in just one short three-month cycle before the end of a generation, particularly while they're also preparing for the next generation to come in. In that sense, we knew going in that we would be cutting out the last rises of a generation no matter what.
The reasoning for choosing to prevent rises from two shifts instead of one is that, in our current usage-based tiering schedule, shifts happen at the beginning of July and October. This means that we don't have much time at all after July's shifts before the generation ends - only four months - and that means that, if suspect tests or other tiering action are necessary, the time tier leaders have for them is very limited. While as Ortheore pointed out, tiering action is possible in old generation lower tiers now and they never truly "die" as long as people are still playing them, they do almost always see extremely low activity once a generation ends, only being played occasionally in annual tournaments. For this reason, we feel it's best to give tier leaders more control over the tier in its final months so that they can leave it in an enjoyable state for everyone.
Also, the reason we're only targeting rises and not drops (aside from that being the scope of this thread) is that drops are much more within a tier leader's control. You can prevent a broken drop from terrorising a tier via banning it, but can't prevent the rise of a staple to another tier.
We did discuss this too. We essentially decided it was best to just cross this bridge if we come to it; TPCI's never delayed one before, and we know that as the world's biggest media franchise, they have a lot of fans and investors alike to adhere to. It's unlikely we'll ever see a significant delay on a mainline game, so it's not really worth accounting for.
So, as an official rule: going forward, the final 2 tier shifts of a generation will only feature drops and not rises. Thanks to everyone who discussed.
While we understand some counterarguments (i.e. lower tiers getting potentially harmed near the end of a generation is just the nature of usage-based tiering), we all collectively agree that as a group of fans striving solely to have the most fun we can with our metagames, it is undesirable to have any of them left in a disliked or potentially even near-unplayable state. Situations like SM PU Mesprit are somewhat rare, but they are also very unfortunate and completely avoidable; there is no real reason for a playerbase to need to "fix" a tier in just one short three-month cycle before the end of a generation, particularly while they're also preparing for the next generation to come in. In that sense, we knew going in that we would be cutting out the last rises of a generation no matter what.
The reasoning for choosing to prevent rises from two shifts instead of one is that, in our current usage-based tiering schedule, shifts happen at the beginning of July and October. This means that we don't have much time at all after July's shifts before the generation ends - only four months - and that means that, if suspect tests or other tiering action are necessary, the time tier leaders have for them is very limited. While as Ortheore pointed out, tiering action is possible in old generation lower tiers now and they never truly "die" as long as people are still playing them, they do almost always see extremely low activity once a generation ends, only being played occasionally in annual tournaments. For this reason, we feel it's best to give tier leaders more control over the tier in its final months so that they can leave it in an enjoyable state for everyone.
Also, the reason we're only targeting rises and not drops (aside from that being the scope of this thread) is that drops are much more within a tier leader's control. You can prevent a broken drop from terrorising a tier via banning it, but can't prevent the rise of a staple to another tier.
One question that I don't have an answer to, however: what happens if the next generation's game is delayed after the cancelled shift? I don't know if Pokemon games have ever been delayed, but its not really out of the possibility. Do we just deal with it and delay all future shifts?
We did discuss this too. We essentially decided it was best to just cross this bridge if we come to it; TPCI's never delayed one before, and we know that as the world's biggest media franchise, they have a lot of fans and investors alike to adhere to. It's unlikely we'll ever see a significant delay on a mainline game, so it's not really worth accounting for.

So, as an official rule: going forward, the final 2 tier shifts of a generation will only feature drops and not rises. Thanks to everyone who discussed.