Provide ability to deploy and activate master pages to the host web using the app model
One thing that we still use Sandboxed solutions or FTC for is the deploying of branding assets such as master pages. Although, there are some hack-like approaches that you can use with CSOM, a more direct supported approach would be nice.
It would be nice if the model would also set the master page on the host web as well since this is a common piece of code we write as a feature receiver as well.
Since you can upload and activate a master page on the host web using CSOM/JSOM/REST APIs, we consider this scenario to be possible with the existing APIs.