It would probably be stupid if we could drive coaches on citybus lines in Berlin
Not only it would feel weird, it would also look unrealistic.
However, there can be other ways to implement coaches from Fernbus/Tourist Bus into The BUS.
My idea is to make a special shuttle bus line that would take passengers from Berlin's Tegel Airport to somewhere in the City Centre like the main Bus Station (A direct chartered route). Another idea could be to take passengers from, for example - a school, to the Berlin Zoo by coach Maybe some business trips from the City Centre into the suburbs? There's definitely a few options if TML wants to take that route