I suggest generating higher level "Category collections" or Searchable series names for related games in the directory to allow sub-searching and filtering for streams across multiple closely-related games.

I suggest adding an additional tab to the Browse directory page right by "Categories, Live Channels," and title that something like Collections or Series to allow browsing for streams that are categorized within a collection of games in the same franchise and allow filtering that view of streams by any tags.

These "Game series" or "Category collections" would be more specific than looking for a category by 'Category Tags,' but this allow easily browsing for all streams in multiple games of the same series within a single browse action by the viewer.

For example: have a general "Pokemon" category group available to click on when browsing Stream category collections to start browsing for all streams playing ANY of the large number of Pokemon games, and allow filtering by other tags from that view: instead of having to choose between picking the name of one Pokemon game to click on (or being stuck filtering from all categories). Another example would be a "Zelda" category group to browse for all streams playing any Zelda game; "Mario" for all Mario games, and so on.

This would be helpful to avoid hiding streams from the directory in Low-traffic categories that are related titles from a larger popular franchise from discovery that penalizes high-viewership streams for trying out less-often played entries in the series (For example, Zelda: A Link between worlds usually has 0 streams, so it is unlikely many people will browse that specific category.).

There are many different Zelda/Pokemon games, and the current Directory search and browse tool is frustrating if looking for streams across All Pokemon games specifically filtered down by tags of choice, because the Directory pages on Twitch currently have no option to search, filter, and browse for multiple games of Specific categories at the same time to capture all related games in the same search results.

I would propose that "Category Group or Game Series" be an added optional free-form text the streamer could enter like tags (and it is in theory possible some games would be related to two series and not just one).

But if the Game series is one of the most popular and known to Twitch based on enough streamers entering the same Series name in connection with a category - it could be automatically set to the series name when playing a game in known series, so Twitch could suggest a game collection name for some games, but hold off on placing the actual game Series as a searchable element in the directory until a sufficient number of streams with a sufficient number of viewers are active in that series.