This prototype already can detect major, minor and sus chords from a single selected staff. Special attention is paid to the way it detects enharmonic names (double-flats, sharps etc). No user interface is provided/needed besides a single menu entry.
Note: plugin's prototype was written during today, so it lacks some major features. The main things that are not present: detection based on all staffs/instruments and only 4 chord types currently in use (M, m, sus2, sus4). The need for a plugin like this raised when I had to fill the chord names for i-th time by hand and found no plugin that just does the thing. Extract it in the MuseScore's plugins folder, as usual. See http://musescore.org/node/10129 for details on the plugin installation.