There's been some discussion of 4Q521 on the Xtalk list recently and this link has just come up:
Expectations and the Expected One: 4Q521 and the Light It Sheds on the New Testament
Willem-Jan de Wit
It's an on-line version of a thesis submitted for the Dutch equivalent of a Masters-title, which the author received cum laude from the Faculty of Theology at Utrecht University in 2000. It was supervized by Prof. Dr. P.W. van der Horst (Utrecht) and examined by him with Dr. L.T. Stuckenbruck (Durham, UK). It's a good piece of work, especially at Masters level, though I would have liked to see a more nuanced discussion of the source-critical issues involved in the section on 4Q521 and Mat 11:2-6 // Luke 7:18-23; de Wit looks at the possibility that Matthew knew Luke, following Hengel's sketch, without looking at the more detailed -- and I would say much more plausible -- view that Luke knew Matthew. But that comment aside, this is a useful piece of work and well done to him for putting it on the web.