There are two features I'd like to have that'd let me not have to manage any tags through iTunes.
In 2.34a, there's no way to find and download cover art without overwriting all of your tags with information from the web source. My tags are fine, and look just like I want them. I just want to grab cover art.
Also in 2.34a, the Alt-T dialog doesn't let you drag images from a web browser into it. iTunes lets you do this, and it's extremely convenient. You can just google image search the album cover, then drag it into iTunes. iTunes downloads and adds it behind the scenes (you don't see it downloading). I'd -love- for this feature to be in MP3Tag. The cover art square in the Alt-T dialog could be the drop target.
In order to make it even more convenient to figure out which files need cover art, it'd also be nice if there were a way to display a column in the main display that indicated whether cover art is embedded. It'd be even nicer if I could work out a way to only display files that do not have cover art embedded.