I am guessing Thor 4 will be Hemsworth final Thor Movie and will show him finding a way to settle the remaining Asgardians and put them on some type of path to rebuilding a legacy.
I also suspect, he will do a few cameos or co lead in the 'Revengers' aka Asguardians of the Galaxy aka Guardians. Not sure if they will try to bring in Professor Hulk for more Buddy stuff or if they save Hulk to introduce the FF4 and maybe Namor as I am not sure how many more movies he has in him?
I also think Jane Foster as Thor is coming in the stage as much as that will anger many. the reports are she has expressed openness to returning to the role with some of the more recent treatments she has been shown, after a long period of saying she was done with it. I am guessing donning the mantle of Thor is the enticement.
Natalie Portman just gave us the tiniest sliver of hope she'd return to the Marvel Cinematic Universe
...The ball is in your court, Marvel! If the comic book brand decides to give her a call tomorrow, who knows if Jane Foster could finally fulfill her destiny of
picking up Mjolnir and becoming the Goddess of Thunder when Thor is forced to retire? This is the kind of
Thor content the world needs right now....