A much easier solution for Twitch would be to simply add a TTS option directly into chat. This way, the streamer wouldn't have to send out another stream. The feature would just be baked into the chat itself. They could even add customization features like "Read Names" or "Read Symbols" so things like names and symbols can be included or excluded as the user sees fit.
I'm vision impaired myself, so I'd really like a feature like this to be added so that when I'm streaming I can just listen to chat instead of having to fully rotate myself to my other monitor in order to read chat which makes it almost impossible to play a game while also paying attention to chatters. The ability to hear chat would allow me to keep playing my game and not have to look away. PLEASE ADD THIS TWITCH!

This is a fantastic idea not only for providing a TTS service for visually impaired people, but also it could also allow improved accessibility for people with audio sensory processing issues, and have an adverse reaction to repetitive and/or loud alerts. I am 100% certain there are streamers out there who would appreciate being able to cater to more of their viewers with a feature like this, without having to change the experience for the rest of their viewers.

I'm guessing that this could be achieved by building upon the existing setup that lets streamers split off their live stream audio from the VOD: Allowing streamers to pipe an audio stream without alerts to Twitch, and letting viewers select a specific one to listen to - in a similar way that they can pick a set visual quality. That would require some changes on the frontend stream player too, but it seems doable.

You know this is a great idea, and never really thought of something like this. I know this is an older idea but posting to hope it gets more attention.

This is a very useful idea, and in addition I also agree with Schfiftyfive55's suggestion below of being able to control the audio tracks from the game, music and voice separately on the watcher's end if possible.

I support this suggestion. I would add that my reasoning differs slightly. Please split the audio tracks by broadcaster voice/BC music track/game audio feed.
Some of the streamers I really enjoy watching have not the best music they listen to in my opinion. I think this suggestion could be a part of the main suggestion of this thread.

Twitch should invest more in accessibility feature like this one!
I am doing a PhD that aims to improve accessibility of live streamed gaming with audio description (gametospeech.com). I tried to contact Twitch about my PhD several times without any success reaching someone. Twitch should work on innovative ways to provide accessibility features instead of just stating in their Accessibility Statement that it is not feasible…

This feature would not only be a great addition for those with varied levels of impairment but also allow streamers to add dimension to levels of interaction with audience. The freedom to switch between hearing the chat (TTS) and normal audio would allow streamers to respond while focusing on complicated tasks. This will result in new and completely interesting topics to be explored on stream.

I play Go, an ancient Chinese board game, and just implemented a voice that reads out move coordinates as they're played. I would LOVE to be able to output this to a separate audio channel that can be accessed by whomever needs or wants it.

Honnestly its frustrating beeing unablee to not be able to read the chat windos...doing a stream without comunicating with thee people in your streem sound useless to me. So yes a TTS is aabsolutly a must and by the way if its like a voiceover on iphone it can reads eemoticone as well it does for letters and sybols. So yes a multi audio track would be very great or an toggle on and off TTS with volume control that all blind and visually impairs needs. I would do live streams but withoout comunity interaction its pointless...so i hope it will appear soon on both pc and mobilee.

I do believe that an incorporated Text to speech reader option would be useful, especially if it ignored emoticons.

Don't know if anyone else is trying to use screen reader for chat but in my opinion the badges make the chat reader unusable if you were actually visually impared. need a way to make screen reader not read the link and badges for visually impared people. Has anyone else investigated this?

I think a better solution would to be to have the option to change the font size for the chat. I partake in streaming and if you connect your OBS to twitch you can have the chat next to the screen that shows what viewers see on stream. Within the OBS chat setting, you can change your font size easily and I've found myself keeping yup and actually be able to read chat easier. If only the Twitch site had this option cause I wouldn't need to zoom in the website and increase the size of the font.

I was just about suggest they add the ability for streamers to have multiple audio tracks, and for viewers to then be able to mute / change the volume of those on their own, say for people that don't want to listen to the stream's music or game sound.

OBS already supports multi-track audio so in theory, it should be possible to make a second track available on Twitch.