As far as I know club income from TV rights is significant only in the Premier League. Therefore, Frankfurt would be happy to remain in their current position only because 4th place provides a direct ticket to the Champions League where the club's income is significant. But it will be difficult for them to hold this position as Dortmund are behind, plus Union Berlin will probably get back in business and play well again.
The 4th standing of the Bundesliga is very good enough in my opinion because they could surely enter the UEFA Championship League, but surely Union Berlin and Dortmund will keep on buzzing in for some payback for me, there is likely little chance for these two teams to move forward 1st Dortmunds list of injuries and suspension, and with Union Berlin, I think they just got lucky at the beginning of the season, so it is highly unlikely that Frankfurt will lose that position this is just what I see, maybe a shifting position with RB Leipzig could be a possible outcome for now, but further development I will still see to make sure,
Dortmund is not playing well this season. So, I really do not know if they will be able to get themselves into the top four positions or not.
But Dortmund should be able to get ahead of Union Berlin. Because Union Berlin is also not playing well. They could not continue the way they started the season. So, I think they will go further down on the table.
I am not sure about Dortmund. It is really hard to see if they will actually be able to improve or not because they are going through some big difficulties right now. Frankfurt is actually showing good performance. And their performance is actually more stable compared to Dortmund. So, I think Frankfurt will be able to hold onto the position that they are in right now.