Well, even now it's still too early to decide on the championship but for the mid-season and the end of the season too I don't think there will be much change here as the only possible additions are Dortmund and Leipzig which every year they are always in the Champions League zone and join the competition.
Last season there were a few other clubs that could have been in the mix but for now dark horse clubs like Freiburg and Union are still underperforming so maybe they will be excluded now.
For VFB they had a great start to the season and we saw that they improved a lot this season but in the last few games we saw how they started to have problems so I would also rule them out.
It definitely too early to decide the champion, so many things have changed in this season just as if they substituted each other, take a look at union Berlin that finished last season in fourth position are now in last position when match is still in 11 game while VfB Stuttgart that were battling not to relegate are now sitting comfortably in third point living behind second runner-up of last season with two points interval and Leipzig in the fourth position have one point in between, VfB Stuttgart performance this season show how serious the want to make it to champion league next season.
As I said overall though it is too early to predict about the top 4 but for the championship then Bayern will be irreplaceable and that is something that I think is almost certain because however looking at the situation now for other clubs only Leverkusen can keep up and most likely in the middle of the season the most change will only be in Dortmund and Leipzig who are slowly returning to their form and are in the top 4. After that nothing else is expected because in the end no matter how hard the clubs in the bundesliga try it still ends up staying the same where Bayern is always the favorite and difficult to replace in the first position while becoming the champion again and again.