The biggest things I can think of that might fit that window of time are the adding of "bits" (a more streamlined way of donating to streamers) and Twitch Prime

The biggest things I can think of that might fit that window of time are the adding of "bits" (a more streamlined way of donating to streamers) and Twitch Prime subs (where Amazon Prime customers get one free sub per month to assign to a streamer of their choice). Arguably the latter might be more attributable to Amazon rather than Twitch itself.