I first noticed this with the plugin Quick-Cache, which activates without problem, but doesn't shows up anywhere. Its menu it's simply not there. Found why, and became aware of the conflict, in the forums.
Problem is that the plugin does all the capability checking using
edit_plugins, removed by the constant...
Now I found that the plugin Search and Replace also bugs with the constant.
I just added this information to the Codex.
And would like to search for alternatives to enabling DISALLOW_FILE_EDIT.
map_meta_cap, obviously, doesn't works.
What I can think of is removing the submenu item, the action link and, case someone lands in
/plugin-editor.php by a direct URL, make the editor window read-only.
I already assembled this code and will post as an answer, but would be glad to know this community opinion and other possible approaches.