MIDI's issues in a notation context are twofold: non-standardization of controls for e.g. choosing articulations for string instruments, and an inability to communicate future information if known to the MIDI producer - say, for instance, knowledge that this Note On event is the beginning of a phrase that will last for 2 measures, as known to notation software.
There's a real way in which MIDI solved for communicating trigger events over the wire, but was not extensible enough to allow for further backwards-compatible standardization that would let it communicate music over the wire. By contrast, the web evolved from communicating hypertext to sending entire application environments and executable code over the same protocols. The web was born later, to be sure, but in an age where an Arduino can execute JavaScript, I wish we were looking to much more extensible modes of communication as inspiration for what can be done with interoperable musical devices.