This is the immediate thought one gets, I can guarantee you that Twitter considered this. It surprises me that parent was deemed insightful.

Should what parent suggests be announced I expect it would be in place for about six minutes (+/- 5) before we'd see the first Tweet with the actual message in the form of a URL.

  http://example.com/Hi_this_is_a_tweet ...

And as someone else stated, long messages are clearly against Twitter's concept/principles/idea/whatever.

The interesting part about this is that instead of URL shorteners we'd end up with domains that would just act as decoders of the link you clicked on. Good or bad, who knows.

And while we're at it, let's think of the next step: It wouldn't be long before someone implemented a packer/cruncher on these messages to be able to squeeze them into a 140 character limit so that it can fit into an SMS. Then we'd realize that this is a remarkably stupid thing to do and start sending un-shortened links to blog posts again. Profit!