Thanks! That's interesting too - lifting the public tweet limit would also fundamentally change Twitter. As an author of tweets, I think I'd like it. I think @byuu mentioned it would promote intelligent discourse on important subjects - I agree.
As a reader though, I don't want to lose the high-bandwidth nature of Twitter. The headline thought/status/caption in your stream, with a link to the details hits an information consumption optimum for me.
It's really that first DM in a conversation where I think 140 characters causes me to leave Twitter. Maybe I'm doing it wrong - often trying to stuff salutation + context + question into the first DM. If the convo gets past that, then yeah, 140 is fine.