And how will you solve brigading? All it takes is two large groups disagreeing on something, and your reputation goes down the drain if you're in the slightly smaller group.
An accounts "history" and "reputation" will be tied to each site. A liberal who posts regularly on echo chambers on both sides of the aisle will have a middle of the road reputation. On Fox news for example you'd see next to their comments:
FoxNews.com Rep: -123 Global Rep: 38
A high global rep is due to the high score posting comments on WashingtonPost articles. Where you would see:
WashPost.com Rep: 161 Global Rep: 38
I'd expect someone with a reputation of 0 to be an honest individual gaining views on both sides of an argument. Someone with a global rep of -1833 is probably a troll or someone who doesn't interact with "like-minded" people, which could of course be seen by looking at the history of where the reputation came from.
You as a consumer, would most likely flag site reps to show on all pages, so maybe you on every site you visit would see a users reputation like so regardless of the site you are on:
Current Site Rep: 3 FoxNews.com Rep: 283 WashPost.com Rep: -87 Global Rep: 221
And you could, of course, dig into their history of reputation, and even Hide/star particular users who you notice are trolls/note-worthy to you personally.