You can download whatever you like as far as I am know, lots of app's already do this (like apps that have subscriptions, read books, play audio etc)
They do tell you what they think bad content is Content Policy but they don't much care how you get it (Embedded or Downloadable) as long as you follow a couple of rules which are basically don't surprise the user with huge downloads, let them opt out etc.
Google also just added a new service to allow you to automatically download a expansion pack which can be up to 2GB and can be hosted on their market servers Google Expansion Packs
They also have made the down loader and zip compressed access source code available so that you could use it as an example if you want to host offsite data by making some modifications.
Expansion packs have some (in my opinion) quirky requirements and the device must have Google play vs. Google market installed on it, but it's a freebie way of hosting some fairly big data.