Unlike saving a file, reading a file is a basic function of EmEditor, and it has to read a file anytime while EmEditor is running. If EmEditor needs to elevate itself, it should stay as elevated status all the time until EmEditor closes. This situation is also dangerous when EmEditor opens other files at the same time.
Furthermore, I believe it is a very rare case, so I wouldn’t put much effort to enable this kind of situations. Rather, I would like to put that effort to something else more important to other people.