1) Will a minimum number of endorsements lead to groupthink? Will a substantial, polite but unpopular comment still get endorsed?
2) If this works initially and improves comments immediately, could it have negative long term affects? Will new users find it confusing or intimidating? Will people comment less knowing that others are less likely to see it?
And one question:
Why not have comments with 0-3 upvotes only visible to people with 1000+ karma? Isn't that the same thing as the endorsement system?
Worthy experiment, regardless.
0-3 upvote hiding would massively inflate karma, as you'd have a minimum of 3 karma for every "acceptable" comment. Not to say it couldn't work, as the karma source is then at least slightly filtered, but it would change the fact you can post a ton of average but not inappropriate comments and maintain close to zero karma.
I believe it will likely kill decent and valid discussions. HN already is a little disconnected from reality sometimes, with this we will end up with a fake consensus. Besides, it will become harder to attain 1000+ karma, so we will be endorsing a small group of people of old users and will be unwelcoming for new folks.