Twitch TV will start charging for high end streams.
There are 2 types of subscriptions on Twitch.
Some streams (usually high-production tournament events) have required that you subscribe to their stream, to access 720p and up. In this scenario, the highest res you were able to get for free was 480p. Since there is now no longer a 480p transcode, the best you will be able to get is 360p. The vast majority of streams on Twitch on any given day are not these types of events with this subscription model.
The vast majority of streamer on Twitch are individuals. They often have subscriptions you can purchase too. However, from most cases I've seen, they dont lock HD resoultions behind the subscription paywall, instead they tend to offer things like the ability to chat, or custom chat icons etc. In this situation, your resolution options will remain unchanged (unless you specifically liked watching at 480p).