It would be great to use just one program to manage my digital audio. Unfortunately, there are some features in other programs that still haven't made it to MJ that are really useful for those who have large collections. This is by no means an exhaustive list but are the ones that if MJ8/9 supported them, would make it so I wouldn't have to go elsewhere for them.
It would be great if MJ supported:
1. The ability to swap fields. Artist <> Title, Artist <> Album, Album <> Title, etc. Of course the best thing would be the ability to create your own, but I use these defaults a lot. Unfortunately, especially with compilations, it's a crapshoot which comes first, artist or title. I know I can change these around in the rename preferences, but it would be a lot faster to just do them all the same way and swap the ones that need to be swapped.
2. Some sort of indication that file names are too long for Joliet. (I would think this would be part of the new burning engine. Is there a way to use the Smarlist feature to show all filenames over 64 chars?)
3. The ability to look up tags without a CD. (I think this is already in the works!)
4. Track number formatting 0X, 00X, XX/XX, XX.
Supporting the above would mean I could dump Tag & Rename. I'm sure there are other features that others would want, but these are the ones I use.