I think that would be a good idea to reward a viewer after watching enough ads.
I often leave a stream because there are too much ads and it's frustrating.

So we could give for each viewer a "contribution wallet" that fills while watching ads, then after we reach a certain amount, we can sub on that specific channel using the time spent watching ads.

No need to see a value like money/time generated, it could be a progress bar with a % and when we reach 100% we can "sub for free".

For example, let's say I am watching two channels, let's call them A and B.
Let's say that, in that example, we need to generate 10$ while watching ads, to get our reward subscription.
After a week spent on each stream, I got like 5min of ads on channel A and 15 min of ads on channel B.
If, for example, 1min of ad generates 0.50$.
We would have 2.5$ generated on channel A. Which would give us 25% of our progress bar.
And we would have 7.5$ generated on channel B. Which would give us 75% of our progress bar.
So watching 5 more minutes on channel B would allow me to get my reward and get my sub for my fidelity.

So instead of changing channel to avoid ads, I could watch a streamer I like, knowing that each time I am filling my progress bar to finnaly get my sub, thanks to my fidelity.