one click migration
If you remember the desktop era, before the web2.0, and so before the web app era, it was quite easy to migrate from applications to applications. If you take the example of an ODT document, you can read/edit it from different software (OpenOffice, LibreOffice, Microsoft Office, Zarafa..). And you can read/edit them from different platform also like linux, windows, android.. So at this time, migrating your data was not really a problem. You put them in a drive, put this drive in a new device, and you just need a software to read/edit it, and that's it.
When the web transformed into applications, it introduced a great bug! Suddenly your data were tied with your application far from your control. Unhosted web app is trying to solve this by decoupling data and application on the web. But in the mean time, we need to work on hosted web app.
There is also an other issue related to web application. The format is always tied to this web application. So usually, to transfer your data between related applications, you need some kind of conversions. As an example, you have wordpress providing importers for other blogging applications like tumblr.
And applications like wordpress provide an exporter/importer, but it never works fully, and even when you are migrating from wordpress to wordpress, you always need to manually tweak it. Plus this exported file doesn't contain your domain name nor your SSL certificate.
So in the particular case of the Indie App Store, the first implementation will probably provide wordpress and known. It would be important that people will be able to migrate their data (from known for instance) between implementations of such a store, but also between web hosting providers.
Even thought unhosted web applications are coming and wordpress is already offering importer/exporter tool, it would be a greater good for the user of such a store to have access to a one click migration feature.
Then to make this feature available to the Indie App Store, we need to define what Migration Format is for web applications.