I am aware that this has been suggested more than once before. If I recall reading this right: Twitch has elaborated that the Turbo sub fee would not cover the costs of transcoding for Turbo subs... Back when the Turbo sub fee was $8.99. It's going up shortly to $11.99 in the USA with no additional features to justify the price hike. Give Turbo subscribers transcoding options, YouTube offers it for FREE.