There are a lot of problems with reification. It's a real strait-jacket. It would kill the JVM as a platform for Clojure and Ruby and kill some of the advanced parts of Scala.
I talked with Vlad Ureche (from the EPFL Scala Team) about this very topic a few months ago after Scala Days Berlin. He said that some Scala features would not be possible to implement on the CLR because of its restrictive generics implementation. So while JVMs generics type erasure is a pain, it seems to give more room for innovation on the language level.
Unfortunately I did not understand the specific reasons he gave, but it had to do something with reification.
