I was talking about this with another member, and thought it would be cool to open this up for everyone else in a proper topic.
By my estimates, which are usually a month or two off, I have the following release dates for what I call primary Generation releases, when the primary wave of 20 or more Pokemon of that generation are released.
Gen 5: August 2019
Gen 6: June 2020
Gen 7: April 2021
There’s a 10-month gap (give or take a couple weeks) between many of these releases (the only exception being the one between Gen 1 and Gen 2 (July 2016 - Feb 2017, 8 months), but Gen 3 and Gen 4 were each 10 months apart from their respective previous generation, so I’m going by that. It’s usually based on that there are 9 Legendaries (one each month) and a couple of returning Legendaries from previous generations to fill in the gap.
As far as their releases, I do believe that the tiered released system will continue to be used, but that in Gen 5 we will see larger waves as Gen 5 boasts 151 new Pokemon, 9 of them Legendaries, and 3 Mythicals, which means that 139 Pokemon would be selected for the tiered releases. That’s the largest available since Gen 3. Very few of these Pokemon require evolutionary items or stones, only 10, and two of them are using items we already have (Sun Stone). This could be the easiest release of all, but likely have a large amount of regionals since there are many non-evolving Pokemon (13 in total, 4 of them paired). Gen 5 is likely going to be the best release due to the relative ease of release that the PokeDex suggests.
Gen 6 will likely be more interesting as it has only 3 Legendaries and 3 Mythicals, and also totaling only 72 new Pokemon, the fewest in any generation up till now. Eevee’s final evolution debuts here, and a few more unique-item evolutions are here as well, but for the most part, it’s fairly an easy release. If a tiered-release happens here, it will likely be only 10-20 at a time, much like Gen 4 right now. The scarcity of new Legendaries will likely be overshadowed by a large number of returning Legendaries with new Shinies to fill in the spaces. We could be seeing some very unique Special Research Quests, particularly for Zygarde and Hoopa.
Gen 7 is going to be a weird one. 7 Legendaries, 3 Mythicals, but the introduction of Ultra Beasts (9 total) will make this extremely crowded. It’s hard to believe that the Ultra Beasts won’t be Raid Bosses in some shape or form since they share Legendary-like stats. 88 total new Pokemon are available, but only 69 are non-Legendary or non-Ultra Beast. No evolutionary items are required this time around.
What are your thoughts for the future of Pokemon GO Generation releases? What do you expect?