I just noticed someone made a Script for that, can't find out who it was, but i guess i may share that script with you:
https://dl.dropboxusercontent.com/u/...20Zoom.eel.zip
Place this script in your Reaper script folder
Open Action List
Click button: Reascript: Load
Navigate to the script and choose it.
The script is now imported into your Reaper Action list.
Assign it to a selfchoosen keycommand
- In Arrange, select a midi item and hit that keycommand.
MIDI editor will be opened, zoomed in to the notes in the midi item.
Hope this helps !