I'm thinking about Python and C/C++ combination to replace the original concept about OSGi + Java + JNI + C/C++ in our SW architecture.
I definitely don't need to replace all features of such OSGi frameworks as Felix or Equinox.
What I really will need in my Python code:

Enabler of modularity for the application layer
Component-based framework for applications
Central registry of services/components 
Very lightweight framework, it will run on embedded devices (though pretty enough of RAM)

Can you please advise on such Python framework?
Peter already mentioned Apache Celix. Might be well worth to check it out. Part of Celix is a Remote Service Admin (RSA) implementation, making it possible to use it in a distributed environment. Eventually this implementation will also make it possible to communicate with a Java based OSGi framework, making Celix+RSA an alternative for JNI. This has the additional benefit that the native and java code don't share the same process. If one end runs into a problem, the other end still stays running.
In line with Celix, you could as well look at Native-OSGi, this is an effort of Celix and some C++ OSGi like frameworks (CTK Plugin Framework and nOSGi) to come up with a combined approach for Native OSGi like implementations. This includes stuff like a well defined API, bundle format, code sharing etc. 
Looking at your requirements I thinks Celix and Native-OSGi might be a good fit.
Python framework as an alternative for "Java + OSGi" combination