It would be nice to disable the preview thumbnail for a recently released title. Often when a new game comes out many streamers that I follow play it. For some games (particularly story driven titles) the preview thumbnails might contain spoilers.
So what if you had the option in your setting to disable the preview thumbnail for a period of time around a games release? For example any time before the official release and for 2 weeks after. It could be replaced with just about anything really, the streamers profile pic, the game's logo, a black screen, etc...
The idea is for thumbnails to have a spoiler mode, so that I can scroll through my following list without spoiling games like Danganronpa V3 via thumbnails. Spoiler mode would allow the broadcaster, to make it so that their thumbnail doesn't display without being hovered over.
Instead of the thumbnail their could just be a Twitch Logo or something similar that says spoilers, or maybe just picture use for the game, with the word Spoilers overlayed onto it.
Alternatively, and this could be useful for other purposes, allow broadcasters to set their own thumbnail. However, this would probably defeat the purpose of thumbnails.