It's a simple task. Given the artist and title, show all albums or EPs or compilations that contain that song. Allow the user to choose.
A really sophisticated program could use the audio content to match a recording and then show all occurrences, without even asking me for the artist or title.
MP3Tag is not alone in its inferiority - none of the programs I've tested can perform this simple task except MetaTogger, and it can't write the information it has found back to the file's tags, because it has a bug.
Where would I find these scripts, and how do I incorporate them into the program? Even though this should be core functionality, given the low quality of all the competitors, I'll certainly consider attempting to augment MP3Tag....