Portability is less new than originally expected. It means that if I move to another provider, there is no detrimental approach in practice. The Article 29 Working Party has adopted guidelines recently. They appear on one point to be controversial with regard to the interpretation of article 25 of the GDPR, because the GDPR says that portability only relates to data provided by the business. We know and experience shows that many other data are on the device or are accessible to the provider, to the controller, although they are not, formally speaking communicated by the data subject. This is an area of limbo where the Article 29 Working Party has decided to consider this area as part of the portability.
On June 13th, 2017. See this statement in context.