Yes, we absolute NEED this!
What I consider to be my serious games (where I concentrate the most) are Standard Live chess games. These are the games I'd like to search through. I'm sure others feel the same about blitz. For these games, there is no way to check back and see how you've faired in a particular opening. We need this to see where our errors are and how we can improve.
I don't know if this has been discussed before, but wouldn't it be cool to have a game explorer for all chess.com games? I'm sure the database is there (as it's just a combined feature of all the mygames explorers) so the implementation shouldn't be too hard.
I don;t know if it would be useful for anything but it seems like a really fun option.