Just a short post to testify that the new feature “number of visible tracks” is a really good shot ! Thanks to all devs 
It is mentioned here http://manual.ardour.org/ardours-interface/the-zoom-controls/
(I was searching for vertical zoom), but I don’t know where to find it… A menu somewhere?
Vertical zoom for editing Midi tracks its so essential, I need more explanations in the manual… Best would really be either the menu/path or even better a picture. There are too many options in such a complex program…