(However, couldn’t Podium just always put imported MIDI tracks inside a single audio-capable master track so that it works automatically and is structured like normal arrangements?)
It could, and I may change this some day. Some users may work exclusively with MIDI, and so would not need the master audio track.
I think it would also be good if Podium supported horizontal mouse-wheel scrolling. Some mice support tilting the scroll wheel left and right to scroll horizontally. Standard windows controls seem to support this. Could Podium also support this so that such users can easily scroll horizontally in the arrangement editor?
I remember testing this a couple of years ago, and was not happy with the result. I have a mouse with side-tilt, but it provides horrible accuracy.