Concerning Autocomplete - definetly needed!
But there is a much more serious problem with multi-genre / multi-artists (or all other multiple meaning tags) - synchronistion with portable players.
I myself am a proud owner of serious music collection, MediaMonkey Gold Membership, and a Creative Zen Vision : M. And the moment MM3 got a multi-genre support I started reviewing and resystematizing my library in order to have an album art stored in each mp3 file and an exhaustive ID3 description, wich I defined to me as:
1. Artist Tag - full list of artists involved in a track production, in order to get rid of "feat." in a title tag and a track to be findable by any artist (well, where I feel like it

)
2. Album Artist Tag - a compilation or label title here (like Hed Kandi, or Ministry of Sound)
3. Genre - a list of appropriate genres, describing track. So that, driving a car, I could just select one and hear all the songs in that style
(besides title and album of course)
Example: The "Just Feel Better" song from Santanas "All That I Am" album should contain tags:
1. Artist Tag - Carlos Santana;Steve Tyler
2. Album Artist Tag - Carlos Santana
3. Genre - Pop;Rock;Guitar
But I've been stupid. I've checked the results in Vista in WMP11 - saw it working, decided that it's OK with MTP devices, and started to work. Later, after one third of my library was structured that way (believe me, it cost me a lot of pain) I tried to update my player with refreshed tracks and got garbage. It does not care about Album Artist Tag at all, and multiple artists/tracks are treated like a
wicked;very;long;named;artist performing in a uniq;unreadable;long;genre. It killed me.
I’m sure that multiple meaning tags have the future, so it is a correct way to organize library anyway. But I wonder:
1. Is there any portable media player in the wild NOW that fully supports multiple tags? Actually I’ve passed a long way choosing a player to meet my demands – Vision : M satisfied me because I can plug it in my command system in a car, and have its interface fully displayed on screen. Now it looks like I need a player that can output its interface AND deal with multi-tags. Does anyone know such a treasure?
2. Because I find it doubtful to find such player at the moment, I suppose I need some kind of a script that would cut off the tag meaning from the first “;” (s/;.*// - Perl speaking) before synchronization to MTP device. (and even reorganize album artist tag (if exists) to artist, and in this case add artist to title like “artist – title“) It’s a wrong way, but I need to have at least some organization in my Zen to be. So does anyone know such solutions?