I think that would be really cool. In my particular case I would like to allow users to upload up to two mp3 files and then edit item.php in my K2 category template using this method 
community.getk2.org/forum/topics/top-tip-for-templating-k2s so i have control over the placement of the extra fields.

 

Hopefully once uploaded the extra field as stored in the database would really just contain the url to the uploaded mp3.

I want to start using jPlayer to play the mp3's so I would edit my item.php and insert the jPlayer code and have each instance of jPlayer reference my mp3 urls from the appropriate extra field...

 

I'm sure I could use the attachments feature in K2 to do this but I could certainly see instances where I might actually want to have the mp3's and use attachments as it was meant to be used. Plus I don't currently know if I can loop through the attachments and edit my item.php similar to the extra fields method. I guess I might be finding out shorty :)