Here's the position of Ecuador
"In the course of these conversations, our country has sought to obtain strict guarantees from the UK government that Assange would face, without hindrance, an open legal process in Sweden. These safeguards include that after facing his legal responsibilities in Sweden, that he would not be extradited to a third country; that is, ensuring that the Specialty Rule [»www.publications.parliament.uk/p···s01.htm]
is not waived. "
It's the same position. I think Ecuador is in the mainstream in demanding that Assange only be tried on what he's being extradited on. Like the other link said, the Rule of Specalization "is to ensure that a person is not extradited on a pretext".
The failure of Britain and Sweden to issue the guarantees increases the chances that Assange is being extradited on a pretext. We'll see what more lawyers have to say, but I find the Ecuadorian position persuasive.