I think it would be nice if all characters get more voice lines added. Especially for characters like Noir Lime who only has hit and death sounds. And hopefully voices for holiday events, like giving a voice line for the Android SLC-56 to sing the Jingle Bell song, that would be hilarious and perfect for special holiday events and features.
As well should also include voice lines for co-op and tdm, where allies can mention other characters and interact while the player is still battling, etc.