Thanks d'aniel. My initial feeling is that Turing-completeness is not necessary for bitcoin and would very likely lead to unforeseen problems and instability (mostly related to the halting problem). Money isn't a computer.
I moved this question about risks with turing complete scripting to this thread on turing complete / ethereum and added some comments.
https://bitcointalk.org/index.php?topic=431513.new#newAdam