a) it WILL kill off those who want to remain (pseudo/ano)nymous and create throwaway accounts for discussing sensitive stuff (like the multiple "my startup is failing" posts in the last months)
b) Sorry, but I (and many others) have actually lives to live and jobs to do. 1000+ karma users are not moderators, and many simply will be too lazy / too occupied to click "endorse" all the time.
c) Discussions live on the "live" part - and <1000 karma users will have to endure MASSIVE waiting times, effectively killing discussions.
Well any site with community based content is going to fail if users don't interact with it. "Endorse" will just be the equivalent of upvoting something if it hasn't already been endorsed. It's not an onerous burden.