If you arbitrarily take $50k as a living wage then it's basically the top 2000 streamers who can make a living on Twitch. Random googling tells me there were approximately 8 million active streamers in September. Again arbitrarily assuming that 7 million of those are 'casual' and doing it for fun that means the percentage of streamers making a living wage is 0.002%.
Back of the napkin math but kinda depressing.
Edit: Someone on Twitter told me that Affiliate status is pegged around the top 3% of streamers. So taking that as my new baseline for "trying to make it" since you can actually get paid out, it raises the percentage to a whopping 0.008%!