Ad revenue on Twitch still amounts to next to nothing compared to other revenue, at least for streamers. I have to assume that carries on to Twitch itself, as well. Ads just are not financially tenable online for the most part, and with good reason - they're dumb and people don't like them, they at best are unnoticed and at worst are between the consumer and their desired content which almost always casts them in a negative light. Google gets around this with Adsense and such by owning half the internet and being, essentially, the gateway, gatekeeper, and key all in one for the majority of western people.
Personally, I hate Twitch's video browsing/searching entirely, and also they are SUPER aggressive about DMCA stuff. I watch creators like CGP Grey and Prozd on YouTube and YouTube is also my go-to music platform because I can find songs on there I can't find anywhere else online. It's hard to imagine that experience marching over to Twitch, but we'll have to see. Patreon is essentially providing the subscription part of Twitch for YouTubers (or anyone technically) but it doesn't much help YouTube itself in doing so. YouTube (Google) could buy Patreon and implement it into YouTube or just make their own version of it but there's no signs of that being a thing that is underway. Instead I keep getting suggestions on my phone to subscribe to YouTube Red (terrible choice of name) and YouTube Music and I have no idea what the differences are or why I would do either considering I'm still able to use YouTube the way I like without them.