In general, metagame change is driven largely by a cycle of reacting and adapting to the broken set of the month. Basically, a new threat that's almost very hard to deal with in the current metagame shows up, whether because of Nintendo changing the Pokemon themselves, Smogon changing the tiers to shuffle things around, or somebody figures out a tough-to-crack set that can take on most of the major threats at the time. The first one's pretty obvious, and is usually a huge and permanent change to the metagame.
As for the other two? The metagame immediately reacts as half the community puts that set on their team, teams that get completely destroyed by the new set vanish overnight, and everyone else tries to balance their lineup between countering that one set and doing whatever else they want to do. If an efficient counter is found, that one becomes popular until the set it's meant to counter begins to decline in use, causing the metagame to swing into a new equilibrium which is similar to before but with the newly discovered sets added to the long list of things people must consider when building new teams.
If no efficient counter is found without massive changes to all teams, then there's almost immediate outrage as people feel that the metagame has been broken, and that Pokemon is quickly moved up one tier, resulting in a slight change in the metagame as things that dealt with that Pokemon's older and less effective sets decline in use, and some people attempt to adapt the moveset that owned the game to other, weaker Pokemon.
In general, however, it's really difficult to discuss each change individually in a vacuum (except possibly really major ones stemming from Nintendo massively changing things) as I suspect some part of this thread is trying to look at it. First, because the metagame is a huge, constantly changing creature with thousands of sets in use at any given time. Second, even people using established sets often use customized variations - between personal preference and the demands of the team, it's nearly impossible to track the metagame in terms of single changes as people usually do.
For example, while I don't know modern Ubers at all, you mentioned Wish Blissey gaining popularity lately...you blamed that on countering Kyogre, but I think it's part of WishBliss's overall popularity surge (even mentioned in the Blissey strategy page) due to the offensive shift brought on by especially Platinum, along with the fact that it seems like Wish would be a good idea in general to have on an Ubers team to ensure that your beefy beasts are impossible to whittle down once you've taken out their counters.
As for the other two? The metagame immediately reacts as half the community puts that set on their team, teams that get completely destroyed by the new set vanish overnight, and everyone else tries to balance their lineup between countering that one set and doing whatever else they want to do. If an efficient counter is found, that one becomes popular until the set it's meant to counter begins to decline in use, causing the metagame to swing into a new equilibrium which is similar to before but with the newly discovered sets added to the long list of things people must consider when building new teams.
If no efficient counter is found without massive changes to all teams, then there's almost immediate outrage as people feel that the metagame has been broken, and that Pokemon is quickly moved up one tier, resulting in a slight change in the metagame as things that dealt with that Pokemon's older and less effective sets decline in use, and some people attempt to adapt the moveset that owned the game to other, weaker Pokemon.
In general, however, it's really difficult to discuss each change individually in a vacuum (except possibly really major ones stemming from Nintendo massively changing things) as I suspect some part of this thread is trying to look at it. First, because the metagame is a huge, constantly changing creature with thousands of sets in use at any given time. Second, even people using established sets often use customized variations - between personal preference and the demands of the team, it's nearly impossible to track the metagame in terms of single changes as people usually do.
For example, while I don't know modern Ubers at all, you mentioned Wish Blissey gaining popularity lately...you blamed that on countering Kyogre, but I think it's part of WishBliss's overall popularity surge (even mentioned in the Blissey strategy page) due to the offensive shift brought on by especially Platinum, along with the fact that it seems like Wish would be a good idea in general to have on an Ubers team to ensure that your beefy beasts are impossible to whittle down once you've taken out their counters.