TLFT is, initially, a mobile app (iOS/Android) which allows you to send tweets longer than the current 140 characters right from your phone.
It will NOT replace your tweet with a link to long-form content on an external site. It WILL allow you to see the full text from within the standard Twitter application.
It's a very simple workaround that I'm very surprised isn't out there already.
There is not much money to be made out of it at this stage, I would imagine it would be an ad-supported freemium model to start with, with the possibility of adding pro features if it got enough traction.
This is more of a kudos project... as in, we would both get lots of kudos from the Twitter community if we did it. But if there are any iOS/Android developers out there looking for a small project to their teeth into to get started in the world of App Store and Play Store.