The same career path as a professional athlete. Some go into commentating, some go into sports management, and most retire broke and have to pick up a whole new career in their late 20s/early 30s.
Twitch streaming can be extremely practical if you're being sustainable about it. Assuming you're actually watching your income and expenses and being smart about when to hire on additional help you can make a pretty darn successful career. I'd point to T90[1] as an example of someone that isn't near the top 1% but has built an extremely sustainable business including paid moderators and content editors (for sending clips to YouTube).
The skills and experience they've picked up directly translates to a number of "practical" careers: affiliate marketing, social media marketing, PR, community building, video and audio editing, etc. not to mention game-related careers in eSports, game development, etc.
