I couldn't agree more. If you're going to break compatibility, do it for a good reason. Type annotations, that would appeal to scientists(BTW, a lot of them are using Cython)...
http://www.python.org/dev/peps/pep-3107/
(More specifically, Python 3 includes generic "function annotations" that look a lot like type declarations do in other languages, but can be used for other purposes as well. The idea is to offload typechecking to a library, so you could eg. include type inference, dimensional analysis, preconditions or DBC, etc. as desired.)