Another option would be to turn lengthier posts into cards. Uses existing Twitter concepts, doesn't change anything for existing users, lets people express more complex ideas. Seems like an easy change and a big win for everyone.
Still, I don't quite know if I like that idea. I guess we'll see.
For reference, here's what 10,000 characters looks like:
In figuring itself out now, Twitter's real problem that its existing users haven't had to experience any real degree of change for a long time. Facebook was kind of smart to "move fast and break things" and ignore the complaints from people who don't want to have to learn new ways of doing things :P