I don't agree that twitter popularity lies on how easy it is to publish on it but in the fact that it establishes a reading contract. I know exactly how much time reading a single tweet will take me so I can read them in many circumstances.
That's why I think apps like TwitLonger make no sense.
The point is not to remove a functionality but to further constrain a contract (and enforce it).
The problem is that you are trying to enforce it on top of an existing platform with a use case for which it doesn't really make sense.
If you really don't want to receive long emails from strangers you can always add a filter in your mail setup that deletes any email over 500 chars long from people not in your address book with an autoreply that says "I don't read anything over 500 chars long".
The point is not to remove a functionality but to further constrain a contract (and enforce it).