Comment by al_borland

This mainly just requires the ability to export, and standard formats. For generic file storage, emails, contacts, calendars, etc, this is largely possible already. Though there are minor incompatibilities based on various implementations or customizations on top of the standard.

The big problem comes into play for new, or more custom types of applications. It takes a while for something to become ubiquitous enough that standard formats are developed to support them.