Okay, just a fun speculative topic. Feel free to agree or disagree!
I think that Jessa may be headed for a life as a Bates. Why? Just a few things I have noticed.
#1 - She (out of all of the girls) has decided to take up both mandolin and guitar. Both are string instruments none of the other J'girls are seen on, but that Zach and Lawson Bates are frequently seen playing. While the rest of the girls posed with their violins for the outdoors big family portrait that Scott Enlow took, Jessa chose to hold her mandolin.
#2 - Jill mentioned when the Bates came to visit them in Little Rock that Jessa had been the one to come up with the idea to decorate their rooms.
#3 - She and Michaela are close friends. Whenever the Bates & Duggars are together, she and Michaela are usually together. It hasn't been noticed as much as the Jana and Erin friendship but it is there. And Michaela is very close to her brother Zach. A little pre-courtship matchmaking going on?
#4 - When the Duggars arrived at Big Sandy a couple of years ago, and met up with the Bates much was made about the fact that John David was kind of standing across the room from Erin and that the cameras seemed intent on focusing on their reactions. However, I also noticed that both Zach and Lawson immediately moved over to where the older girls were standing and both seemed to mill around the Jessa, Erin, Jana crowd a little.
Obviously this is not the strongest evidence! But hey it's fun to contemplate! I do think that one of those 4 older girls is going to become a Bates. There has just been too much build up on the show for a courtship not to happen would be anticlimactic.