[Answer]-Running django on GAE + Cloud SQL, with third party reusable django apps ( like South)

Sorry, but at least South and django-compressor would not run on GAE.

GAE is a completely different platform. Yet you have SQL access to your tables, it’s just an abstraction layer over a nonrelative database. There is no filesystem access, but there are tons of other limitations. Even Django itself could not be run on GAE without patches – you have to use special version, django-nonrel.

I would suggest to read more GAE documentation so you can decide if a particular application could be run there or not.