The following posts were made by reddit user UsedToThrowaway to share with us some insight into South Park's performance in Season 20 and possible effects on future seaesons.

October 27, 2016 - Would like to share some information about this season and the outlook Comedy Central has on South Park right now...

I created this throwaway because I am an active Redditor on my normal account and do not wish to be associated with this post.
There is a growing sense of disappointment within the Comedy Central HQ about the current format of the show. As a business standpoint, this is not ideal for the network. The quality has seemingly dipped over time and a lot of those higher in the network are becoming frustrated that they cannot play reruns which hurts their ratings as well as outreach to a newer audience. What I mean when I say is they can't play reruns is that with the current format, you can't play the 5th episode of the season and have someone who is not a South Park diehard understand what is happening.
The contract extension that was signed in July of 2015 was before anyone knew they would change their format. As you know, Matt & Trey and all involved often wait until the last moment to decide on what to do. The network feels this has drastically hurt them in regards to the new format because they don't have a solid plan for the show. This is all a crapshoot right now. That would be fine in older formats, but they risk having huge plot holes and having things not make sense.
The rating have dipped. The season opener for the season had high expectations and met that because a lot had to do with old viewers tuning in to see what kind of show it would be. Ratings actually did increase slightly over the next few shows but the last 2 episodes have been considered a failure by audiences. This is expected to level out or drop off and not rise as people who have missed an episode or two now are completely out of the loop and are expected to just "give up" on it in a sense.
The ratings drop is a bit worrying. This is the quickest it has dropped in the shows history. For majority of the seasons, the trendline has increased through the shows season but this does not look like it will happen this year.
In a poll given out by CC, people did not favor the direction of the show and had a below average outlook on main characters such as Cartman and Randy who scored the lowest they ever have. Butters has dropped, Kyle has dropped while the only character popularity to rise was Gerald.
The network will always support the show, but they really are not happy with what is going on with it and I personally would expect that maybe by 2018 they switch formats back to how it was.
Just passing along what I have to share because I often see debates on here about the new vs. old format and want to give a basic idea to everyone what is being said behind the scenes.
CC is unhappy is the amount of episodes they play from the last 2 seasons. You won't see many repeats being aired. This has nothing to deal with the Hulu deal. CC just feels that nobody will watch a single rerun of the new episodes.

December 8, 2016 - Not to 'toot my own horn' but I am the CC employee who warned you a couple of months ago this would happen to South Park.

No more season-long formats confirmed. CC and Matt&Trey agreed it had run its course and wasn't moving the show forward any longer.
I said all there is to know. They are going back to the old format. Comedy Central and Matt&Trey agreed the direction of the show was not working and are going back to the old format. I posted that 41 days ago, what happened between then was they let the season finish and reviewed the numbers. The decision to do this was made previous to episode 9.
Hint: the episode names "Not Funny" and "The end of serialization as we know it" weren't accidents.

February 9, 2017 - We could possibly see 12 episodes this upcoming season.

There are some early talks going on that they may extend this season by a few episodes. This is VERY EARLY in discussions and I personally don't believe it's going to happen but it has been brought up and talked about. Possibly 8 random episodes in the old format with a mini series at the end for the Holidays.
I know people would favor this so I just thought I'd pass it along and hopefully it does happen. I know that majority of people preferred having random episodes and then a mini 3-4 episode series at the end.