This goes well with allowing multiple categories, too.

PLEASE. What if I want to find someone playing any pokemon game? I would have to search every game separately! People who play the older games on twitch aren't seen as often as people playing the newest game, and I think that's unfair.

I know this is an old idea.... but this idea is still today really good. I would love for this to be implemented.

The fact that franchises such as Mario, Legend of Zelda, COD, DOOM, Sonic, NBA 2K, Madden, etc, don't have branching categories is levels of astounding that cannot be fathomed.

Having branching categories allows for more varied discovery. Having the top overall....let's just say, Pokemon...streams featured in a carousel at the top of the page, followed by directories that lead to different games in the franchise would help immensely.

****, even for the Retro Category, there should be distinction by platform (i.e: NES/Famicom, SNES/Super Famicom, Genesis/Mega Drive, Saturn, PlayStation, Arcade, etc.)

Touhou already had an easily accessible general category(At least until Twitch messed that up), so it makes perfect sense for other big franchises to get general categories

Yes please! Overarching Pokemon category with subcategories or specialised tags for more specific games...

Due to many people streaming main series Pokémon RPGs (Red/Blue, Emerald, X/Y, Sword/Shield, etc.) under the most recently released Pokémon game even though that would be classified as streaming in the wrong category, I think what would be best would be to group all mainline Pokémon RPGs into one existing category. This would include the following games:
Red, Green, Blue, Yellow, Gold, Silver, Crystal, Ruby, Sapphire, Emerald, FireRed, LeafGreen, Diamond, Pearl, Platinum, HeartGold, SoulSilver, Black, White, Black 2, White 2, X, Y, Omega Ruby, Alpha Sapphire, Sun, Moon, Ultra Sun, Ultra Moon, Sword, Shield, and any future main series releases.

I would keep spin-offs in their own separate category, but if needed can also be streamed under this as well.

Pokemon GO is a separate category as well.

I really really like this idea! When I played Pokemon I did indeed always just go to the latest release due to often playing multiple generations of Pokemon being played at the same time or just because most people searching for Pokemon just want to have a nice chat instead of caring what Pokemon is played!

I also noticed that indeed with bigger franchises like Zelda, Mario and the Soulsborne games I do not really mind which one I am watching, making multiple categories an absolute mess.
Instead I just wish there was a way to click on the franchise and see ALL the streams within that franchise like Jerry written down above. Would actually make me use the searching options within Twitch to search for streams for once.

Game categories should be based on their franchise, and then have their individual games as a "sub-category."

For example, the category would be "The Elder Scrolls," and the sub-category/game would be "Skyrim"; The category would be "Pokémon", and the sub-category/game would be "Sword/Shield".

That would eliminate people needing to play out-of-category, because they can just play under "Pokémon."

Multi-user Dungeons (MUDs) have dedicated communities, and thousands of games are out there for the entire world to play. It would be beneficial to add a category specifically for MUDs or text-based games generally, classics like "Zork" or popular MUDs like "Aardwolf."