Short answer: No.
Long answer: Still no. Subversion does have the concept of "externals". You can map a directory to (a part of) another repository and every time you update you will also get the changes from the other repository. However, a Modeler project looks like a monolithic binary file to subversion and there is no directory that represents a module. That is why externals cannot be used for this purpose.
In the future we will, however, look at better ways of keeping modules that originate from the App Store up to date but that something for another day.