Understanding the principle, I would be worried that it has the perverse effect to reduce the pvp player base. It is very easy to imagine someone with a negative reputation to stop playing. It is also possible the people would be deterred by the fact that they can be rated negatively.
To me, this game is not about being elected the prom queen. This game is about playing a superbly designed card game. I fear that I would lose interest if there was a bitching component added to it. That being said, I do have favourite people to play against and others that I avoid. That's fine like that and I assume I'm not everyone else's favourite either, so they avoid me. That's fine like that, no change required, in my opinion.
You could be right, and I agree for the community here it may not bring value.
But in general reputation systems have been seen to be positive over time, and of benefit to larger communities (see how Stack Exchange revolutionised the online Q&A systems for example)
And if we imagine the number of players growing to a hundred times the current number, it might be a useful thing.
Having said that maybe Valentino was only talking about rating the player skill level, whereas I've expanded that into general "reputation".
Imagine if down the line there are some people who seem to enjoy starting a game and then just quitting out, to be annoying, over and over again. A reputation system might help mitigate things like that.
So it's really not to make the reputation thing part of the game or some sort of popularity contest (the world has enough of that as it is IMO :)), but is really about creating consequences for negative behaviour.
In any case, although technically simple such a system has a lot to it and we won't be adding it within the foreseeable future - and I would only do it if it were part of a generalised platform and then only if there were several other interesting customers available already. So we are talking very blue-sky here :)