It would be really helpful for new streamers or even the old streamers to see the viewers retention for a particular category, so that people have more data about viewers and so they can better decide what category to stream. It would also help creators to get an idea of how a new category (for example a new game) is performing in terms of views increase/decrease.

A simple short little example according to my manual calculations is:
For example: There is this new game that is still in beta called DEADLOCK, and it shares quite a lot of viewers from VALORANT, so it would be helpful if a person can see the valorant viewers increase/decrease over a certain period of time, for example I have done per day calculations to know whether VALORANT viewers are increasing or decreasing here are the results:

VALORANT:
Nearly a month ago:
Average viewers/day: 75K
Total followers: 19.6M
Average viewers to follower ratio: 0.38%
Average channels: 1700
Average viewers/channel: 3

Now:
Average viewers/day: 55K
Total followers: 19.6M
Average viewers to follower ratio: 0.27%
Average channels: 1500
Average viewers/channel: 4

DEADLOCK:
Nearly a month ago:
Average viewers/day: 1.5K
Total followers: 15K
Average viewers to follower ratio: 10%
Average channels: 74
Average viewers/channel: 6

Now:
Average viewers/day: 5.5K
Total followers: 60.4K
Average viewers to follower ratio: 9.1%
Average channels: 200
Average viewers/channel: 10

So clearly this gives a person an idea that valorant has a viewership decline, this could lead in two ways, one that number of channels streaming valorant are decreasing as well which may or may not be benificial for a new streamer and on the other hand the viewership is also decreasing which also has its pros and cons for new or old streamer. So people might wanna explore further to know what other categories are performing well. Although this is a rough estimate but, if we had some graphs that shows the category performance overall then that would be more helpful for people to decide what to stream and what people really wanna see, and I am sure that TWITCH must have that data already for their own analytical purpose since these type of user behaviour data is important.

I think its already getting long so I am going to end this up here (sorry for a long message) although I do have some more really lengthy ideas as well which could improve new streamers satisfaction and also could make viewers life easier as well as they get to see what they want to see, but I am uncertain about whether even this post gets read by someone or not, so I'll leave those ideas for now and see how well this post gets recognized first.

Ps. I am sorry I made anything confusing here since I am not a native English speaker so I may have had some trouble in explaining what I wanted to mean, so hopefully (fingers crossed) TWITCH team knows what I mean to say here.