I agree that we really need a way to read/write binary data. I have already thought about doing a PR to add such functionality to graphical arrays. It would be as simple as adding a flag to the [read( and [write( methods.
In theory, it would be possible then to implement a MIDI file reader/writer as a Pd abstraction. But to be honest, I think only a masochist would do that :-)
On the other hand, mrpeach's [midifile] has always served me well and it's one of those things that don't really get obsolete.
So I don't think that Pd really needs built-in MIDI file support. After all, even a kitchen-sink language like Supercollider doesn't come with built-in MIDI file support.