I honestly don't see how a social network can survive without retweets. They're just not going to get the critical mass. There needs to be an "amplify" gesture and quote ain't it.
Disagree :) The thing that's breaking other social media is that the social part is getting removed.
Forcing you to write words and actually come up with an opinion instead of pressing a "repost" button without any context provides a much richer social experience.
I see your point, however my take is that each obligatory text of a quote will create low-signal high noise mess that people don't have time to read. The comment is rarely as important as the thing it comments about.
And people will find their way around it. Very soon it will become mainstream to quote with a simple . or a space to work around the system.